14379...99127 (87-digits)

This number is a prime.

                                                          1437981 9517246113
8521036839 3452692517 4073733425 9640879028 1553797956 6704703072 0519999127

A prime number that can be expressed as (17⁷¹ - 1)/(17 - 1) and curiously uses only the digits 1 and 7 to do it. Note also that the number starts with a 1 and ends with a 7. [Post]