Is (2⁵⁸+1)/5 an integer? A prime?

I'm not a computer expert, and had a glitch with mine - so used calculator to reach 29th power -- then did rest by hand. Good exercise to do something like this once in awhile - and got 288230376151711744 the first time; + 1 = this sum, ending in 5, and
an integer, not prime, divisible by 5.

Posted by CharleyA. on 2007-04-12 00:14:58