Prime numbers | Factors and multiples | Pre-Algebra | Khan Academy

Prime numbers | Factors and multiples | Pre-Algebra | Khan Academy


In this video, I want
to talk a little bit about what it means
to be a prime number. And what you’ll
see in this video, or you’ll hopefully
see in this video, is it’s a pretty
straightforward concept. But as you progress through
your mathematical careers, you’ll see that there’s actually
fairly sophisticated concepts that can be built on top of
the idea of a prime number. And that includes the
idea of cryptography. And maybe some of the encryption
that your computer uses right now could be
based on prime numbers. If you don’t know
what encryption means, you don’t have to worry
about it right now. You just need to know the prime
numbers are pretty important. So I’ll give you a definition. And the definition might
be a little confusing, but when we see
it with examples, it should hopefully be
pretty straightforward. So a number is prime if
it is a natural number– and a natural number, once
again, just as an example, these are like the numbers 1, 2,
3, so essentially the counting numbers starting
at 1, or you could say the positive integers. It is a natural number divisible
by exactly two numbers, or two other natural numbers. Actually I shouldn’t
say two other, I should say two
natural numbers. So it’s not two other
natural numbers– divisible by exactly
two natural numbers. One of those numbers is itself,
and the other one is one. Those are the two numbers
that it is divisible by. And that’s why I didn’t
want to say exactly two other natural numbers,
because one of the numbers is itself. And if this doesn’t
make sense for you, let’s just do some
examples here, and let’s figure out if some
numbers are prime or not. So let’s start with the smallest
natural number– the number 1. So you might say, look,
1 is divisible by 1 and it is divisible by itself. You might say, hey,
1 is a prime number. But remember, part
of our definition– it needs to be divisible by
exactly two natural numbers. 1 is divisible by only one
natural number– only by 1. So 1, although it might be
a little counter intuitive is not prime. Let’s move on to 2. So 2 is divisible by
1 and by 2 and not by any other natural numbers. So it seems to meet
our constraint. It’s divisible by exactly
two natural numbers– itself, that’s 2 right there, and 1. So 2 is prime. And I’ll circle
the prime numbers. I’ll circle them. Well actually, let me do
it in a different color, since I already used
that color for the– I’ll just circle them. I’ll circle the
numbers that are prime. And 2 is interesting
because it is the only even number
that is prime. If you think about it,
any other even number is also going to be
divisible by 2, above and beyond 1 and itself. So it won’t be prime. We’ll think about that
more in future videos. Let’s try out 3. Well, 3 is definitely
divisible by 1 and 3. And it’s really not divisible
by anything in between. It’s not divisible by 2, so
3 is also a prime number. Let’s try 4. I’ll switch to
another color here. Let’s try 4. Well, 4 is definitely
divisible by 1 and 4. But it’s also divisible by 2. 2 times 2 is 4. It’s also divisible by 2. So it’s divisible by three
natural numbers– 1, 2, and 4. So it does not meet our
constraints for being prime. Let’s try out 5. So 5 is definitely
divisible by 1. It’s not divisible by 2. It’s not divisible by 3. It’s not exactly divisible by 4. You could divide them into it,
but you would get a remainder. But it is exactly
divisible by 5, obviously. So once again, it’s divisible
by exactly two natural numbers– 1 and 5. So, once again, 5 is prime. Let’s keep going,
just so that we see if there’s any
kind of a pattern here. And then maybe I’ll
try a really hard one that tends to trip people up. So let’s try the number. 6. It is divisible by 1. It is divisible by 2. It is divisible by 3. Not 4 or 5, but it
is divisible by 6. So it has four natural
number factors. I guess you could
say it that way. And so it does not have
exactly two numbers that it is divisible by. It has four, so it is not prime. Let’s move on to 7. 7 is divisible by 1, not 2,
not 3, not 4, not 5, not 6. But it’s also divisible by 7. So 7 is prime. I think you get the
general idea here. How many natural
numbers– numbers like 1, 2, 3, 4, 5, the numbers
that you learned when you were two years old, not including 0,
not including negative numbers, not including fractions and
irrational numbers and decimals and all the rest, just regular
counting positive numbers. If you have only two
of them, if you’re only divisible by yourself and
one, then you are prime. And the way I think
about it– if we don’t think about the
special case of 1, prime numbers are kind of these
building blocks of numbers. You can’t break
them down anymore they’re almost like the
atoms– if you think about what an atom is, or
what people thought atoms were when
they first– they thought it was kind of the
thing that you couldn’t divide anymore. We now know that you
could divide atoms and, actually, if
you do, you might create a nuclear explosion. But it’s the same idea
behind prime numbers. In theory– and in prime
numbers, it’s not theory, we know you can’t
break them down into products of
smaller natural numbers. Things like 6– you could
say, hey, 6 is 2 times 3. You can break it down. And notice we can break it down
as a product of prime numbers. We’ve kind of broken
it down into its parts. 7, you can’t break
it down anymore. All you can say is that
7 is equal to 1 times 7, and in that case, you really
haven’t broken it down much. You just have the 7 there again. 6 you can actually
break it down. 4 you can actually break
it down as 2 times 2. Now with that out of the way,
let’s think about some larger numbers, and think about whether
those larger numbers are prime. So let’s try 16. So clearly, any number is
divisible by 1 and itself. Any number, any natural
number you put up here is going to be
divisible by 1 and 16. So you’re always
going to start with 2. So if you can find anything
else that goes into this, then you know you’re not prime. And 16, you could have 2 times
8, you could have 4 times 4. So it’s got a ton
of factors here above and beyond
just the 1 and 16. So 16 is not prime. What about 17? 1 and 17 will
definitely go into 17. 2 doesn’t go into 17. 3 doesn’t go. 4, 5, 6, 7, 8, 9 10, 11–
none of those numbers, nothing between 1
and 17 goes into 17. So 17 is prime. And now I’ll give
you a hard one. This one can trick
a lot of people. What about 51? Is 51 prime? And if you’re
interested, maybe you could pause the
video here and try to figure out for yourself
if 51 is a prime number. If you can find anything
other than 1 or 51 that is divisible into 51. It seems like, wow, this is
kind of a strange number. You might be tempted
to think it’s prime. But I’m now going to give you
the answer– it is not prime, because it is also
divisible by 3 and 17. 3 times 17 is 51. So hopefully that
gives you a good idea of what prime numbers
are all about. And hopefully we can
give you some practice on that in future videos or
maybe some of our exercises.

100 thoughts on “Prime numbers | Factors and multiples | Pre-Algebra | Khan Academy

  • August 15, 2016 at 4:13 am
    Permalink

    Cowboy is what I am to her. and I love her too

    Reply
  • September 2, 2016 at 9:43 am
    Permalink

    Thank you so much

    Reply
  • September 19, 2016 at 6:07 am
    Permalink

    thank you now i know about prime numbers

    Reply
  • October 13, 2016 at 6:34 pm
    Permalink

    This didn't help me

    Reply
  • October 19, 2016 at 5:25 pm
    Permalink

    791,159 views, that's prime!!

    Reply
  • November 8, 2016 at 1:43 am
    Permalink

    this video helped me so much I understand prim numbers now thank you

    Reply
  • November 16, 2016 at 3:11 pm
    Permalink

    is 81 and 31

    Reply
  • November 26, 2016 at 5:45 pm
    Permalink

    thanks for the wonderful  class
    just wished
    the sound wasn't soooooooooooooooooo low

    Reply
  • December 4, 2016 at 3:01 pm
    Permalink

    so Prime numbers are only odd numbers except 2 thanks dude ite really helped

    Reply
  • December 8, 2016 at 5:31 pm
    Permalink

    1 is not a prime number

    Reply
  • December 8, 2016 at 5:32 pm
    Permalink

    Prime numbers are when they have 2 factors

    Reply
  • December 14, 2016 at 12:25 am
    Permalink

    do the freaking factor ranbow😌😌😌💩💩💩💩👍👍👍👎👌✌✋✊👊👐☝👆👇👈👉👋👏💋❤💚💋💀👤😪

    Reply
  • January 9, 2017 at 8:31 pm
    Permalink

    I am in in fourth grade and my mom made me a Khan academy account it is so cool

    Reply
  • January 14, 2017 at 1:15 am
    Permalink

    Loved this. Very easy to follow along. You've got a new subscriber.

    Reply
  • January 25, 2017 at 9:38 pm
    Permalink

    Now I really know how to do prime numbers

    Reply
  • January 25, 2017 at 9:39 pm
    Permalink

    You are so good at maths

    Reply
  • January 25, 2017 at 9:46 pm
    Permalink

    I❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️❤️it

    Reply
  • February 4, 2017 at 3:08 am
    Permalink

    thank you… ;w;

    Reply
  • February 27, 2017 at 2:42 pm
    Permalink

    one how know about the editor????

    Reply
  • March 5, 2017 at 1:46 am
    Permalink

    Negative VOTE, due to your Lousy VID!!!

    Reply
  • March 5, 2017 at 1:47 am
    Permalink

    Sooooo, Wut is the Fucking Good in ALL this??? NOTHING!!!!!

    Reply
  • March 12, 2017 at 4:19 pm
    Permalink

    I finally understand what prime numbers are…

    Reply
  • April 25, 2017 at 2:06 am
    Permalink

    2 factors

    Reply
  • May 31, 2017 at 8:12 pm
    Permalink

    man u help me so much.
    you are my HERO

    Reply
  • June 4, 2017 at 5:30 am
    Permalink

    very helpful

    Reply
  • June 4, 2017 at 4:46 pm
    Permalink

    good

    Reply
  • June 12, 2017 at 10:43 am
    Permalink

    Thanks to Khan Academy

    Reply
  • August 25, 2017 at 1:37 pm
    Permalink

    I wonder what annotation software you are using for this tutorial. Love the blackboard feel!

    Reply
  • August 26, 2017 at 7:04 pm
    Permalink

    Get me the NEWS – I should be DIVINE!
    'Cuz I have the Equation… for EVERY Prime!

    Reply
  • August 26, 2017 at 9:37 pm
    Permalink

    5:39 "We now know you could divide atoms, and, actually, if you do, you might create a nuclear explosion."

    I lolled so hard. That made my day.

    Reply
  • September 4, 2017 at 6:15 pm
    Permalink

    In school I didn't understand they whys about math, and so it didn't make sense. Now I see the importance of prime numbers

    Reply
  • September 23, 2017 at 5:04 pm
    Permalink

    51 is not prime

    Reply
  • October 2, 2017 at 9:06 pm
    Permalink

    Iam just watching this for my freaking Test tomorrow 😭😰

    Reply
  • October 14, 2017 at 11:46 pm
    Permalink

    Thanks for the help. TBH, math is stupid.

    Reply
  • October 29, 2017 at 5:15 am
    Permalink

    Cool

    Reply
  • November 10, 2017 at 9:15 am
    Permalink

    You go on the site www.Ex0-SyS.com/ it gives all the existing primes numbers without limit of numbers!

    Reply
  • November 12, 2017 at 5:04 pm
    Permalink

    1 is not prime number

    Reply
  • November 14, 2017 at 10:49 pm
    Permalink

    Prime Numbers from 0 to 16001

    2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,
    103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,
    199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,
    313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,
    433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,
    563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,
    673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,
    811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,
    941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,
    1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,
    1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,
    1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,
    1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,
    1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,
    1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,
    1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,
    1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,
    1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,
    2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,
    2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,
    2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,
    2399,2411,2417,2423,2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,
    2543,2549,2551,2557,2579,2591,2593,2609,2617,2621,2633,2647,2657,2659,2663,
    2671,2677,2683,2687,2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,2749,
    2753,2767,2777,2789,2791,2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,
    2879,2887,2897,2903,2909,2917,2927,2939,2953,2957,2963,2969,2971,2999,3001,
    3011,3019,3023,3037,3041,3049,3061,3067,3079,3083,3089,3109,3119,3121,3137,
    3163,3167,3169,3181,3187,3191,3203,3209,3217,3221,3229,3251,3253,3257,3259,
    3271,3299,3301,3307,3313,3319,3323,3329,3331,3343,3347,3359,3361,3371,3373,
    3389,3391,3407,3413,3433,3449,3457,3461,3463,3467,3469,3491,3499,3511,3517,
    3527,3529,3533,3539,3541,3547,3557,3559,3571,3581,3583,3593,3607,3613,3617,
    3623,3631,3637,3643,3659,3671,3673,3677,3691,3697,3701,3709,3719,3727,3733,
    3739,3761,3767,3769,3779,3793,3797,3803,3821,3823,3833,3847,3851,3853,3863,
    3877,3881,3889,3907,3911,3917,3919,3923,3929,3931,3943,3947,3967,3989,4001,
    4003,4007,4013,4019,4021,4027,4049,4051,4057,4073,4079,4091,4093,4099,4111,
    4127,4129,4133,4139,4153,4157,4159,4177,4201,4211,4217,4219,4229,4231,4241,
    4243,4253,4259,4261,4271,4273,4283,4289,4297,4327,4337,4339,4349,4357,4363,
    4373,4391,4397,4409,4421,4423,4441,4447,4451,4457,4463,4481,4483,4493,4507,
    4513,4517,4519,4523,4547,4549,4561,4567,4583,4591,4597,4603,4621,4637,4639,
    4643,4649,4651,4657,4663,4673,4679,4691,4703,4721,4723,4729,4733,4751,4759,
    4783,4787,4789,4793,4799,4801,4813,4817,4831,4861,4871,4877,4889,4903,4909,
    4919,4931,4933,4937,4943,4951,4957,4967,4969,4973,4987,4993,4999,5003,5009,
    5011,5021,5023,5039,5051,5059,5077,5081,5087,5099,5101,5107,5113,5119,5147,
    5153,5167,5171,5179,5189,5197,5209,5227,5231,5233,5237,5261,5273,5279,5281,
    5297,5303,5309,5323,5333,5347,5351,5381,5387,5393,5399,5407,5413,5417,5419,
    5431,5437,5441,5443,5449,5471,5477,5479,5483,5501,5503,5507,5519,5521,5527,
    5531,5557,5563,5569,5573,5581,5591,5623,5639,5641,5647,5651,5653,5657,5659,
    5669,5683,5689,5693,5701,5711,5717,5737,5741,5743,5749,5779,5783,5791,5801,
    5807,5813,5821,5827,5839,5843,5849,5851,5857,5861,5867,5869,5879,5881,5897,
    5903,5923,5927,5939,5953,5981,5987,6007,6011,6029,6037,6043,6047,6053,6067,
    6073,6079,6089,6091,6101,6113,6121,6131,6133,6143,6151,6163,6173,6197,6199,
    6203,6211,6217,6221,6229,6247,6257,6263,6269,6271,6277,6287,6299,6301,6311,
    6317,6323,6329,6337,6343,6353,6359,6361,6367,6373,6379,6389,6397,6421,6427,
    6449,6451,6469,6473,6481,6491,6521,6529,6547,6551,6553,6563,6569,6571,6577,
    6581,6599,6607,6619,6637,6653,6659,6661,6673,6679,6689,6691,6701,6703,6709,
    6719,6733,6737,6761,6763,6779,6781,6791,6793,6803,6823,6827,6829,6833,6841,
    6857,6863,6869,6871,6883,6899,6907,6911,6917,6947,6949,6959,6961,6967,6971,
    6977,6983,6991,6997,7001,7013,7019,7027,7039,7043,7057,7069,7079,7103,7109,
    7121,7127,7129,7151,7159,7177,7187,7193,7207,7211,7213,7219,7229,7237,7243,
    7247,7253,7283,7297,7307,7309,7321,7331,7333,7349,7351,7369,7393,7411,7417,
    7433,7451,7457,7459,7477,7481,7487,7489,7499,7507,7517,7523,7529,7537,7541,
    7547,7549,7559,7561,7573,7577,7583,7589,7591,7603,7607,7621,7639,7643,7649,
    7669,7673,7681,7687,7691,7699,7703,7717,7723,7727,7741,7753,7757,7759,7789,
    7793,7817,7823,7829,7841,7853,7867,7873,7877,7879,7883,7901,7907,7919,7927,
    7933,7937,7949,7951,7963,7993,8009,8011,8017,8039,8053,8059,8069,8081,8087,
    8089,8093,8101,8111,8117,8123,8147,8161,8167,8171,8179,8191,8209,8219,8221,
    8231,8233,8237,8243,8263,8269,8273,8287,8291,8293,8297,8311,8317,8329,8353,
    8363,8369,8377,8387,8389,8419,8423,8429,8431,8443,8447,8461,8467,8501,8513,
    8521,8527,8537,8539,8543,8563,8573,8581,8597,8599,8609,8623,8627,8629,8641,
    8647,8663,8669,8677,8681,8689,8693,8699,8707,8713,8719,8731,8737,8741,8747,
    8753,8761,8779,8783,8803,8807,8819,8821,8831,8837,8839,8849,8861,8863,8867,
    8887,8893,8923,8929,8933,8941,8951,8963,8969,8971,8999,9001,9007,9011,9013,
    9029,9041,9043,9049,9059,9067,9091,9103,9109,9127,9133,9137,9151,9157,9161,
    9173,9181,9187,9199,9203,9209,9221,9227,9239,9241,9257,9277,9281,9283,9293,
    9311,9319,9323,9337,9341,9343,9349,9371,9377,9391,9397,9403,9413,9419,9421,
    9431,9433,9437,9439,9461,9463,9467,9473,9479,9491,9497,9511,9521,9533,9539,
    9547,9551,9587,9601,9613,9619,9623,9629,9631,9643,9649,9661,9677,9679,9689,
    9697,9719,9721,9733,9739,9743,9749,9767,9769,9781,9787,9791,9803,9811,9817,
    9829,9833,9839,9851,9857,9859,9871,9883,9887,9901,9907,9923,9929,9931,9941,
    9949,9967,9973,10007,10009,10037,10039,10061,10067,10069,10079,10091,10093,
    10099,10103,10111,10133,10139,10141,10151,10159,10163,10169,10177,10181,
    10193,10211,10223,10243,10247,10253,10259,10267,10271,10273,10289,10301,
    10303,10313,10321,10331,10333,10337,10343,10357,10369,10391,10399,10427,
    10429,10433,10453,10457,10459,10463,10477,10487,10499,10501,10513,10529,
    10531,10559,10567,10589,10597,10601,10607,10613,10627,10631,10639,10651,
    10657,10663,10667,10687,10691,10709,10711,10723,10729,10733,10739,10753,
    10771,10781,10789,10799,10831,10837,10847,10853,10859,10861,10867,10883,
    10889,10891,10903,10909,10937,10939,10949,10957,10973,10979,10987,10993,
    11003,11027,11047,11057,11059,11069,11071,11083,11087,11093,11113,11117,
    11119,11131,11149,11159,11161,11171,11173,11177,11197,11213,11239,11243,
    11251,11257,11261,11273,11279,11287,11299,11311,11317,11321,11329,11351,
    11353,11369,11383,11393,11399,11411,11423,11437,11443,11447,11467,11471,
    11483,11489,11491,11497,11503,11519,11527,11549,11551,11579,11587,11593,
    11597,11617,11621,11633,11657,11677,11681,11689,11699,11701,11717,11719,
    11731,11743,11777,11779,11783,11789,11801,11807,11813,11821,11827,11831,
    11833,11839,11863,11867,11887,11897,11903,11909,11923,11927,11933,11939,
    11941,11953,11959,11969,11971,11981,11987,12007,12011,12037,12041,12043,
    12049,12071,12073,12097,12101,12107,12109,12113,12119,12143,12149,12157,
    12161,12163,12197,12203,12211,12227,12239,12241,12251,12253,12263,12269,
    12277,12281,12289,12301,12323,12329,12343,12347,12373,12377,12379,12391,
    12401,12409,12413,12421,12433,12437,12451,12457,12473,12479,12487,12491,
    12497,12503,12511,12517,12527,12539,12541,12547,12553,12569,12577,12583,
    12589,12601,12611,12613,12619,12637,12641,12647,12653,12659,12671,12689,
    12697,12703,12713,12721,12739,12743,12757,12763,12781,12791,12799,12809,
    12821,12823,12829,12841,12853,12889,12893,12899,12907,12911,12917,12919,
    12923,12941,12953,12959,12967,12973,12979,12983,13001,13003,13007,13009,
    13033,13037,13043,13049,13063,13093,13099,13103,13109,13121,13127,13147,
    13151,13159,13163,13171,13177,13183,13187,13217,13219,13229,13241,13249,
    13259,13267,13291,13297,13309,13313,13327,13331,13337,13339,13367,13381,
    13397,13399,13411,13417,13421,13441,13451,13457,13463,13469,13477,13487,
    13499,13513,13523,13537,13553,13567,13577,13591,13597,13613,13619,13627,
    13633,13649,13669,13679,13681,13687,13691,13693,13697,13709,13711,13721,
    13723,13729,13751,13757,13759,13763,13781,13789,13799,13807,13829,13831,
    13841,13859,13873,13877,13879,13883,13901,13903,13907,13913,13921,13931,
    13933,13963,13967,13997,13999,14009,14011,14029,14033,14051,14057,14071,
    14081,14083,14087,14107,14143,14149,14153,14159,14173,14177,14197,14207,
    14221,14243,14249,14251,14281,14293,14303,14321,14323,14327,14341,14347,
    14369,14387,14389,14401,14407,14411,14419,14423,14431,14437,14447,14449,
    14461,14479,14489,14503,14519,14533,14537,14543,14549,14551,14557,14561,
    14563,14591,14593,14621,14627,14629,14633,14639,14653,14657,14669,14683,
    14699,14713,14717,14723,14731,14737,14741,14747,14753,14759,14767,14771,
    14779,14783,14797,14813,14821,14827,14831,14843,14851,14867,14869,14879,
    14887,14891,14897,14923,14929,14939,14947,14951,14957,14969,14983,15013,
    15017,15031,15053,15061,15073,15077,15083,15091,15101,15107,15121,15131,
    15137,15139,15149,15161,15173,15187,15193,15199,15217,15227,15233,15241,
    15259,15263,15269,15271,15277,15287,15289,15299,15307,15313,15319,15329,
    15331,15349,15359,15361,15373,15377,15383,15391,15401,15413,15427,15439,
    15443,15451,15461,15467,15473,15493,15497,15511,15527,15541,15551,15559,
    15569,15581,15583,15601,15607,15619,15629,15641,15643,15647,15649,15661,
    15667,15671,15679,15683,15727,15731,15733,15737,15739,15749,15761,15767,
    15773,15787,15791,15797,15803,15809,15817,15823,15859,15877,15881,15887,
    15889,15901,15907,15913,15919,15923,15937,15959,15971,15973,15991,16001,

    Reply
  • November 16, 2017 at 11:27 pm
    Permalink

    So the answer must be a natural number because if not than 3 can be divided by 2 and equal 1.5

    Reply
  • November 16, 2017 at 11:32 pm
    Permalink

    My math teacher was wrong I'm bout to roast her boi!!!

    Reply
  • November 21, 2017 at 1:34 am
    Permalink

    this guy is trying everuthing to confuse the people's mind. very stupid video

    Reply
  • November 23, 2017 at 9:40 am
    Permalink

    In one video there is an unprecedented demonstration of why and how they make the first numbers to decrease by increasing the numbering of the integers. It's in a bad English spoken but you can understand. Has 27 visitors and 2 like but no comments yet. It seems to me something good indeed … let me know? Because if I'm right she is going unnoticed …
    Thank you. "Prime numbers, maybe now we know something more"

    Reply
  • November 29, 2017 at 8:50 pm
    Permalink

    Don't get it

    Reply
  • December 1, 2017 at 3:31 am
    Permalink

    You guys should do an abstract algebra course. It's really hard to find introductory info on the subject online, and it's essential for basically all of modern number theory

    Reply
  • December 7, 2017 at 5:10 pm
    Permalink

    thank you Sal

    Reply
  • December 24, 2017 at 3:08 pm
    Permalink

    Now I know that 51 is not a prime number.

    Reply
  • February 19, 2018 at 9:49 pm
    Permalink

    😻 oh shoot I'm getting worked up

    Reply
  • February 20, 2018 at 5:17 pm
    Permalink

    Good video!

    Reply
  • March 27, 2018 at 5:03 am
    Permalink

    i finally figured out what prime numbers are after that video, thanks you really helped me there.

    Reply
  • April 9, 2018 at 6:16 pm
    Permalink

    khan academy I bet your not even a licensed academy (if they are licenced)

    Reply
  • April 18, 2018 at 1:21 am
    Permalink

    I have Georgia Milestones for tomorrow it’s the math part, and I’m reviewing thanks

    I also have a tip for prime numbers, my class just looks at the word. We like to see the “i” in “Prime” as “One”, then we look in front of the “i” And theres a “me” So we think as “me” As itself. So then it would be like —>

    Prime
    I+me

    Hope this helped!

    Reply
  • April 22, 2018 at 2:28 pm
    Permalink

    Very Helpful guys must try

    Reply
  • May 10, 2018 at 1:39 pm
    Permalink

    i understood a lot and iam preapering for my exams i understood prime numbers thankyou khan acadmey

    Reply
  • May 20, 2018 at 10:21 pm
    Permalink

    I'm studying for finals and this has saved me!

    Reply
  • May 21, 2018 at 2:21 pm
    Permalink

    Is it just me or am I still dumb

    Reply
  • May 31, 2018 at 8:02 pm
    Permalink

    why did you write natural numbers (1,2,3..) as the definition if 1 isn't a prime number?

    Reply
  • June 17, 2018 at 6:18 am
    Permalink

    is 0 the same?

    Reply
  • June 17, 2018 at 6:20 am
    Permalink

    so prime is only a number that can divide by 1 and itself
    THANKS:D

    Reply
  • June 17, 2018 at 6:24 am
    Permalink

    51 is not a prime number

    Reply
  • June 19, 2018 at 1:47 pm
    Permalink

    I can't understand this

    Reply
  • August 16, 2018 at 7:43 pm
    Permalink

    11

    Reply
  • August 21, 2018 at 4:07 pm
    Permalink

    ……..my roblox user is sora1224795

    Reply
  • August 30, 2018 at 2:37 am
    Permalink

    Thank you Khan Academy!

    Reply
  • September 6, 2018 at 5:15 pm
    Permalink

    Thank you, I skipped class and forgot what prime numbers were. Thanks so much.

    Reply
  • September 7, 2018 at 12:19 am
    Permalink

    Cool

    Reply
  • September 10, 2018 at 8:59 pm
    Permalink

    oi

    Reply
  • September 22, 2018 at 1:28 am
    Permalink

    Paused the video and got 51 correct, go me lol

    Reply
  • September 26, 2018 at 4:38 am
    Permalink

    thank for the video

    Reply
  • September 28, 2018 at 3:54 am
    Permalink

    Who else is watching this in 2018? No one? Okay than that just leaves me then!! XD

    Reply
  • October 12, 2018 at 11:51 pm
    Permalink

    I'm wanting this for a math test

    Reply
  • October 14, 2018 at 4:16 am
    Permalink

    Wow prime numbers are actually interesting 😆

    Reply
  • October 29, 2018 at 9:38 pm
    Permalink

    How does you write so neat on a computer? That is some neat work!

    Reply
  • November 6, 2018 at 11:00 pm
    Permalink

    u just helped me with my homework lol i had no idea what prime numbers were!Your vid helped tho.

    Reply
  • November 25, 2018 at 11:09 pm
    Permalink

    51 is not a prime number I say so

    Reply
  • December 1, 2018 at 3:06 pm
    Permalink

    is 150 prime

    Reply
  • December 3, 2018 at 7:26 am
    Permalink

    Thank you so much this HELPED

    Reply
  • December 6, 2018 at 4:29 am
    Permalink

    Helps when trying to attain heaven ty

    Reply
  • December 10, 2018 at 10:32 pm
    Permalink

    Hi bro. I found out two fonctions can generate prime number under 100. But over that numbers alot of constraintes should be considerated… too hard..what do you think

    Reply
  • December 18, 2018 at 6:06 am
    Permalink

    0:26 "if you don't know what encryption means…" …then what the hell are you doing here? 🙂

    Reply
  • December 19, 2018 at 1:54 pm
    Permalink

    Long live teachers! 🙏

    Reply
  • December 30, 2018 at 5:48 pm
    Permalink

    Tysm

    Reply
  • January 8, 2019 at 9:50 pm
    Permalink

    this video made no sense at all….. at least to me… iv watched it 5 times.

    Reply
  • February 11, 2019 at 9:27 pm
    Permalink

    WHATS P1^2 + P2^2 – P4

    Reply
  • March 10, 2019 at 2:28 pm
    Permalink

    I hate math but I learn the prime numbers

    Reply
  • March 20, 2019 at 5:05 am
    Permalink

    Thanks

    Reply
  • March 25, 2019 at 11:41 am
    Permalink

    I’m too dumb to understand yay! I will be poor and have unpaid bills when I’m older 🤗 (😭)

    Reply
  • April 8, 2019 at 3:14 am
    Permalink

    Is there a maths equation to figure out prime numbers?

    Reply
  • July 13, 2019 at 2:39 pm
    Permalink

    51 is prime

    Reply
  • August 14, 2019 at 4:44 am
    Permalink

    Got it !
    Thank you!

    Reply
  • August 15, 2019 at 6:41 am
    Permalink

    thank you for this video, i was watching other vids and have no idea what's prime number is and this video helped me understand it well.

    Reply
  • September 1, 2019 at 4:36 am
    Permalink

    I'm not gonna lie
    I'm just here because of JoJo

    Reply
  • September 4, 2019 at 12:31 pm
    Permalink

    1 is not a prime no.

    Reply
  • September 7, 2019 at 12:38 am
    Permalink

    I finally understand what prime number is 👍🏼 yay

    Reply
  • September 16, 2019 at 7:22 pm
    Permalink

    Good

    Reply
  • October 20, 2019 at 2:32 pm
    Permalink

    What if we search for the numbers that can only be build by primes. Like 51. It's build by 3 times 17, which are both primes. Plot these evolved-primes (51 etc.) into the same graph that can show how numbers and primes turns into spirals and later strings when viewing from a bigger perspective.

    Reply
  • November 6, 2019 at 8:54 pm
    Permalink

    Any class mates in ms Pauldins class watching this? Charlotte secondary I'm hendrick

    Reply
  • November 27, 2019 at 5:12 pm
    Permalink

    Thanks in school I wasn't really paying attention I kinda knew what to do but at the same time I was confused so thanks for helping me!

    Edit: You got your self another subscriber

    Reply
  • November 28, 2019 at 6:24 pm
    Permalink

    Thx khan

    Reply
  • November 30, 2019 at 1:18 pm
    Permalink

    Thanks again Sal 🙂

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *