A076234 Numbers k such that sigma(k)/k, sigma_3(k)/k, sigma_5(k)/k and sigma_7(k)/k are all integers.

1, 6, 120, 672, 30240, 32760, 33550336, 459818240, 1379454720, 8589869056, 31998395520, 51001180160, 137438691328, 153003540480, 30823866178560, 796928461056000, 6088728021160320, 212517062615531520, 2305843008139952128, 69357059049509038080, 143573364313605309726720

Offset: 1

Author

Labos Elemer, Oct 04 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..55

Crossrefs

Cf. A000203, A001158, A001160, A013955.

Cf. A007691, A046763, A055709, A076231, A076233.

Cf. A066289 (k divides sigma_m(k) for all odd m).

Programs

PARI

isok(n) = !(sigma(n) % n) && !(sigma(n, 3) % n) && !(sigma(n, 5) % n) && !(sigma(n, 7) % n); \\ Michel Marcus, Dec 26 2013

Extensions

a(13)-a(18) from Donovan Johnson, May 08 2010

a(19)-a(21) from Amiram Eldar, May 09 2024