But second- I was on my way in to work today and thought, "How can you tell if large numbers are prime without having to try every number less than it?"
So thanks to the glorious internet- I found .
He explains the simple rules pretty clearly (and I'm sure there are other, more complicated ones he doesn't provide). But here's the shorthand:
1- Take the square root of the number and drop the decimals.
2- Try to divide the number by the prime numbers equal to or less than the number you got in step one.
3- If none of them divide easily- it's prime!
Example: 137.
1- The square root is 11.704.
2- The primes we need to check are 2, 3, 5, 7 and 11.
3- None of those divide evenly, so it's prime!
Maybe all of y'all knew this, but I thought it was cool shorthand.Statistics: Posted by Kyle — Thu Aug 11, 2016 11:25 am
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