A113286 Numbers k such that S(S(k))=k, with S(n)=sigma(n)/4: 1/4-sociable numbers of order 1 or 2.

30240, 32760, 859320, 898560, 2096640, 2178540, 2234232, 23569920, 45532800, 54996480, 61281792, 142990848, 422688000, 436205952, 1379454720

Offset

1,1

Comments

a(1) and a(2) are 4-perfect numbers (A027687). a(4) = S(a(3)).

a(6), a(8), a(9), a(12), and a(15) are also 4-perfect numbers (A027687). - Michel Marcus, Feb 23 2014

Links

Table of n, a(n) for n=1..15.

Eric Weisstein's World of Mathematics, Sociable Numbers

Prog

(PARI) isok(n) = (type(s= sigma(n)/4) == "t_INT") && (sigma(s)/4 == n); \\ Michel Marcus, Feb 20 2014

Crossrefs

A027687 is a subsequence.

Cf. A113546 (1/3-sociable numbers).

Cf. A355279 (1/4-sociable numbers of order 1 or 3).

Sequence in context: A255752 A254841 A247855 * A355279 A027687 A190475

Adjacent sequences: A113283 A113284 A113285 * A113287 A113288 A113289

Keyword

nonn,more

Author

Yasutoshi Kohmoto, Jan 27 2006

Extensions

a(5)-a(15) added by Michel Marcus, Feb 24 2014

Status

approved