Numbers k such that sigma(usigma(k)) is prime.

A063103

Numbers k such that sigma(usigma(k)) is prime.

Terms

    a(0) =3a(1) =8a(2) =2667a(3) =3937a(4) =57337a(5) =172011a(6) =253921a(7) =677207307a(8) =1073602561

External references