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A113286 Let S(n)=1/4*Sigma(n) . Numbers such that S(S(n))=n, 1/4-Sociable number of order 1 or 2. 1
30240, 32760, 859320, 898560, 2096640, 2178540, 2234232, 23569920, 45532800, 54996480, 61281792, 142990848, 422688000, 436205952, 1379454720 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

a(6), a(8), a(9), a(12), and a(15) are also 4 multiple 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

Cf. A113546.

Sequence in context: A255752 A254841 A247855 * A027687 A190475 A218029

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

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Last modified February 28 01:38 EST 2020. Contains 332319 sequences. (Running on oeis4.)