A sexy prime is a prime number that is 6 more or 6 less than another prime. For example, 23 and 29 are sexy primes. 2 and 3 are not sexy primes, but they are trivial because they divide 6. What is the first prime that does not divide 6, but is not a sexy prime?

I list each prime and the prime that is 6 higher, putting a star instead if that number is composite.
A non-sexy prime will have a star the first time it appears.
5,11
7,13
11,17
13,19
17,23
19,*
23,29
29,*
31,37
37,43
41,47
43,*
47,53
53,59
59,*
61,67
67,73
71,*  Here it is.  71 is not sexy because neither 65 nor 77 are prime.

Posted by Jer on 2011-12-13 10:56:07