25475...67041 (6716-digits)

This number is a prime.

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The generalized repunit (675065¹¹⁵³ - 1)/675064 is prime.

A proof is possible because of the remarkable circumstance that, for b = 5*37*41*89 and p = 2⁷*3²+1, both Phi(p,b) and Phi(p-1, b) are prime, where Phi(n, x) is the n^th cyclotomic polynomial in x. [Broadhurst]