> ... an integer N with exactly 5 prime factors (not necessarily
> distinct) such that 2N+1 also has exactly 5 prime factors:
>
> 688 = 2^4 * 43
> 2*688 + 1 = 1377 = 3^4 * 17
Easy puzzle: what's this?
2 4 52 40 688 4900 63112 178240 38272 5357056 1997824 247221760
586504192 707436544
--
Don Reble djr at nk.ca