The prime triplet (2, 3, 13) is interesting in that it can produce six primes using a product with a sum or difference:
2 + 3*13 = 41
3 + 2*13 = 29
13 + 2*3 = 19
3*13  2 = 37
2*13  3 = 23
13  2*3 = 7
Prove this is the only such prime triplet.
(In reply to
Prime solution by Math Man)
(You left out the possibility of two 2's but this is dispensed of very easily)
You lost me on all of the modular arguments:
If c=0 mod 7, then c=7, but 6c=1, which is not prime.
635=29 which is prime. (I know 2*353 is not but that's not my point.) How you you know c=7 is the only member of c=0mod 7 that you need to check?

Posted by Jer
on 20120519 23:21:10 