17014...05727 (39-digits)

This number is a prime.

                                  170141183 4604692317 3168730371 5884105727

The Mersenne prime 2^127-1 that Édouard Lucas verified in 1876. He is said to have spent 19 years in checking it, by hand. This remains the largest prime number discovered without the aid of a computer. Lucas died under unusual circumstances. A banquet waiter dropped a plate and a broken piece flew up and cut him on the cheek. He passed away a few days later from a bacterial infection (erysipelas).

2^(2^(2^(2^2-1)-1)-1)-1 is prime! [Timothy]