Prime Numbers

[Neueregel]

More Number theory Sal !!

[Goshyouidiot]

I was not expecting to hear about nuclear explosions by watching this video.

[TheSupermodel001]

Wow! Thank you for clarifying that. I didn't really get it the way it was explained in class, but you have definitely simplified this for me. Thank you. Your videos and teaching style usually make math really simple for me:)

[taylor9610]

unlike me

[taylor9610]

sal make some spelling videos some kids don,t know how to spell some words

[BL0XXOR]

@taylor9610 LOL.

[michaelhunter03]

if you know this this is one step in cunputer programing

[ladyjdose]

okay so if 1 is composite and 4 is prime cant you just say that the multi. of 2 are prime and if noot composite>>>?????

[timx2222]

@ladyjdose 1 is an exception. it is not prime or composite.

[pendantry]

Thank you, Khanacademy! :)

[mrbooni02]

thankyou

[usernamessucks01]

3!



[Blitzkreig19]

Nuclear explosion. Lmfao.

[paulceltics]

easy stuff; just remember 2 is an exception

[peacebuntou]

I never got it in as a teenager but i get it now as an adult. Irish i had you as a teacher

[iRockharder]

this is so easy that it's ridiculous that i didn't understand it before.

[Barnekkid]

I hope you'll follow this at some point with a discussion of RSA.

[williampower108]

bivisble

[TheDevilBreaker]

3 and 17 are factors of 51 which in turn dont make 51 a prime number. I just woke up from my dream of math class.

[Goldbergfan91]

When you went on to 6, I thought you were going to lay the seeds for Perfect Numbers. In the future, if you make a video on how to easily test if a number is prime or not, be sure to include the thing about the numbers square root, how you only need to test numbers up to (and including if the square root is an integer) the square root.

[TheOnlyCoolestGuy111]

Yes !!!!!!! im not that "a lot of people" that tricked ! XD hahah

[capteddie]

I'm enjoying your videos quite a bit. I'd love to see more info about prime numbers like different tests for prime numbers. Thanks!

[Waranle]

Finally Sal! Thank youuuuuuuuuuuuuuuuuuuuuuuuuuuu­uuuuuuu

[noxure]

A quick trick to see if a number is dividable by 3 is adding up the decimals and see if the result is dividable by 3, works with every number.

51 -> 5+1 = 6. dividable by 3.

It also works with 9 (and 81)

891 -> 8+9+1 = 18. dividable by 9.

Funny thing is that this means that it doesn't matter what order the decimals are.

198, 189, 981, 918 ,545454, 444555, 554454... can all be divided by 9.

Take a number like 21, add some 3's and 9's in them: 2993333999391 and it's still dividable by 3.

[MuseseekerMan]

Could u make a vid on wave polarization and what is a vector field?

[TheMrNomus]

wooha wooha i've finished your cosmology course now now i don't even know now that course i guess. I'm gonna finish all of them. Thank ou Khan

[AA10Megaviv]

@TheOkham I think very metaphorically they could be considered so.

[Goldbergfan91]

@TheOkham Maybe. Depends on what you define addition and multiplication as under the vector space.

[Goldhugz]

I always thought that 1 was prime... My whole life is a lie.

[Menegoth]

@Goldhugz

Don't worry, complex numbers will make it true again.

[TheOnlyCoolestGuy111]

@Goldhugz hahahahahah hi 5 ! XD

[cool1karan2]

@Goldhugz LOL

[kumogakuredojo]

Lol, I was just doing the exercise for Prime Numbers and had to go on Wikipedia to figure it out. I had no idea it was that new, I just saw that it was recommended for me...

[dishonesttAbe]

Nice video Sal. Maybe you can do a video about the significance of prime numbers.

[GFauxPas]

This video isn't on the khan academy website

[MrDnlyong]

@GFauxPas Good Observation! LOL

[SpoiledLogic]

prime factorization! 

[PEWBLINKPEW]

5th!



[R3mProductions]

LAST!

[shazaduh]

Thanks khan! can you do a proof of infinitude of prime numbers?

[TheKturner05]

Number Theory Videos to come?

[BGood156]

@TheKturner05 I agree, some videos on number theory videos could be very interesting. It would also be a nice way to expose your audience to proof-based mathematics.

[DackIsBack]

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