- NEW!
by Quirkie on July 16th, 2008
It looks prime.
Test: Test for divisibility by primes until prime*prime is bigger than 137.
2: no: it's not even.
3: no: the sum of the digits is not divisible by three.
5: no: it doesn't end in 5 or 0
7: ok, leave that one for later.
11: Add and then subtract each digit like this: 1-3+7. Answer: 5. no: This isn't divisible by 11.
13: 13*13 is 169 which is bigger than 137 so stop.
7: there are clever ways to test for divisibility by 7. But in general they're nearly as complicated as dividing by 7.
So let's just subtract multiples of 7 to see if we can get zero:
137 - 7 is 130
130 - 70 is 60
60 - 56 is 4
4 is not divisible by 7.
137 is prime!
by zeropoint on February 23rd, 2011
137 is a prime number
by yeroco on July 16th, 2008
Yes. Easiest way to tell is to try dividing by all of the prime numbers up to the square root of the number. In this case, the square root is 11 point something. So try all of the primes up to 11 - 2, 3, 5, 7, 11. None of those divide 137 evenly, therefore it's prime.
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Comments
Original and provocative answer -- as usual. Max pts!
by xprofessor on July 16th, 2008