A206036 Numbers n such that sigma(n) = sigma(k) has solution for distinct numbers n and k.

6, 10, 11, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26, 28, 30, 31, 33, 34, 35, 38, 39, 40, 41, 42, 44, 46, 47, 48, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 65, 66, 68, 69, 70, 71, 74, 75, 76, 77, 78, 79, 80, 82, 83, 84, 85, 86, 87, 88, 89, 90, 92, 93, 94

Offset

1,1

Links

Table of n, a(n) for n=1..65.

Example

6 and 11 are in the sequence because sigma(6) = sigma(11) = 12.
7 is not on the list because sigma(7) = 8 and there is no other integer for which sigma(n) = 8.

Mathematica

max = 9000; sigmaList = Table[DivisorSigma[1, n], {n, Prime[PrimePi[max]]}]; Select[Range[Floor[Sqrt[max]]], Count[sigmaList, sigmaList[[#]]] > 1 &] (* Alonso del Arte, Feb 06 2012 *)

Crossrefs

Cf. A066074, A158913, A000203.

Sequence in context: A284350 A333410 A107014 * A349761 A132628 A288928

Adjacent sequences: A206033 A206034 A206035 * A206037 A206038 A206039

Keyword

nonn

Author

Jaroslav Krizek, Feb 03 2012

Status

approved