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

Author

Yasutoshi Kohmoto, Jan 27 2006

Keywords

• nonn
• more

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

• Eric Weisstein's World of Mathematics, Sociable Numbers

Crossrefs

A027687 is a subsequence.

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

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

Programs

PARI

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

Extensions

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