A355279 Numbers k such that S(S(S(k))) = k, with S(n) = sigma(n)/4: 1/4-sociable numbers of order 1 or 3.

30240, 32760, 2178540, 23569920, 45532800, 46475520, 48933360, 50995620, 60933600, 69995520, 72807696, 142990848

Offset

1,1

Comments

a(6..11) = { 46475520, 48933360, 50995620, ..., 72807696 } are the first terms not in A027687 (4-perfect numbers), which is obviously a subsequence.

a(11..12) = { 72807696, 142990848 } are the first terms that are not multiples of 60.

Links

Table of n, a(n) for n=1..12.

Eric Weisstein's World of Mathematics, Sociable Numbers

Prog

(PARI) is_A355279(n, f(x)=if(x && x%4==0, sigma(x\4)))= f(f(sigma(n)))==n*4

Crossrefs

A027687 is a subsequence.

Cf. A113286 (1/4 sociable numbers of order <= 2), A113546 (1/3-sociable numbers).

Sequence in context: A254841 A247855 A113286 * A027687 A190475 A218029

Adjacent sequences: A355276 A355277 A355278 * A355280 A355281 A355282

Keyword

nonn,more

Author

M. F. Hasler, Sep 25 2022

Status

approved