11111...11113 (84-digits)

This number is a prime.

                                                             1111 1111111111
1111111111 1111111111 1111111111 1111111111 1111111111 1111111111 1111111113

The largest prime among the initial one hundred terms in the almost repunit sequence 3, 13, 113, 1113, 11113, etc. The closed form for this sequence is (10 ^ n + 17) / 9, and can also be defined recursively as follows: Define u (1) = 3 and u (n) = 10 * u(n - 1) - 17 for n > 1. [Schiffman]