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A206448 Values of sigma(n) of composite numbers n such that sigma(n) = sigma(d) has solution for any other composite number d in increasing order. 1
24, 31, 42, 48, 56, 60, 72, 84, 90, 96, 120, 124, 126, 144, 156, 168, 180, 186, 192, 210, 216, 224, 228, 234, 240, 248, 252, 270, 280, 288, 294, 312, 320, 324, 336, 342, 360, 372, 378, 384, 392, 399, 403, 408, 416, 420, 432, 434, 448, 450, 456, 468, 480, 504 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

Number 24 is in sequence because 24 = sigma(x) for composite numbers x = 14 and 15.

MATHEMATICA

nn = 600; t = Table[If[PrimeQ[n], -1, DivisorSigma[1, n]], {n, nn}]; t2 = Rest[Select[Sort[Tally[t]], #[[2]] > 1 &]]; Select[Transpose[t2][[1]], # <= nn &] (* T. D. Noe, Feb 13 2012 *)

CROSSREFS

Cf. A206447 (composite numbers n such that sigma(n) = sigma(d) has solution for any other composite number d), A000203.

Sequence in context: A123200 A167307 A161378 * A266984 A217158 A214227

Adjacent sequences:  A206445 A206446 A206447 * A206449 A206450 A206451

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Feb 07 2012

EXTENSIONS

Corrected by T. D. Noe, Feb 13 2012

STATUS

approved

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Last modified July 28 14:04 EDT 2021. Contains 346334 sequences. (Running on oeis4.)