Primes of the form 2*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.

A093938

Primes of the form 2*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.

Terms

    a(0) =2a(1) =277a(2) =2777a(3) =2777777777

External references