12508...40031 (19893-digits)

This number is a prime.

17763*2^66066-1 is prime. Note that 66066 is a palindromic triangular number, and that 1^2+7^2+7^2+6^2+3^2 = 6^2+6^2+0^2+6^2+6^2 = 144 = 12^2. [Earls]