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.

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

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