68647...57151 (157-digits)

This number is a prime.

                                                          6864797 6601306097
1498190079 9081393217 2694353001 4330540939 4463459185 5431833976 5605212255
9640661454 5549772963 1139148085 8037121987 9997166438 1257402829 1115057151

2^521-1 = (2^9)*(2^(2^9))-1 is the largest known prime which is simultaneously a Mersenne prime and Woodall prime. [Rupinski]