77777...77771 (100-digits)

This number is a prime.

                                            7777777777 7777777777 7777777777
7777777777 7777777777 7777777777 7777777777 7777777777 7777777777 7777777771

The largest prime less than a googol and containing only non-composite digits. [Gupta]

The largest prime less than a googol and containing only straight digits. [Gupta]

The one hundredth term in the almost repunit sequence 1, 71, 771, 7771, etc. The closed formula for this sequence is given by f (n) = (7 * 10 ^ n - 61) / 9 and a recursive formula can be described as follows: Define u (1) = 1 and u (n) = 10 * u (n - 1) + 61 for n > 1. [Schiffman]