A076231 Numbers k such that sigma(k)/k, sigma_3(k)/k and sigma_5(k)/k are all integers.

1, 6, 120, 672, 8128, 30240, 32760, 33550336, 459818240, 1379454720, 1476304896, 8589869056, 31998395520, 51001180160, 66433720320, 137438691328, 153003540480, 403031236608, 30823866178560, 796928461056000, 6088728021160320, 14942123276641920, 212517062615531520

Offset: 1

Author

Labos Elemer, Oct 03 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..86

Crossrefs

Intersection of A007691, A046763 and A055709.

Cf. A000203, A001158, A001160, A007691, A046763, A055709, A076233, A076234.

Programs

PARI

isok(n) = !(sigma(n) % n) && !(sigma(n, 3) % n) && !(sigma(n, 5) % n); \\ Michel Marcus, Dec 26 2013

Extensions

a(16)-a(20) from Donovan Johnson, May 08 2010

a(21)-a(23) from Amiram Eldar, May 09 2024