Numbers k such that sigma(sigma(2k-1)) is a prime p.

A247821

Numbers k such that sigma(sigma(2k-1)) is a prime p.

Terms

    a(0) =2a(1) =1334a(2) =1969a(3) =28669a(4) =86006a(5) =126961a(6) =338603654a(7) =536801281

External references