2-hyperperfect numbers: n = 2*(sigma(n) - n - 1) + 1.

A007593

2-hyperperfect numbers: n = 2*(sigma(n) - n - 1) + 1.

Terms

    a(0) =21a(1) =2133a(2) =19521a(3) =176661a(4) =129127041

External references