

A206036


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


6



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
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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 * A132628 A288928 A039509
Adjacent sequences: A206033 A206034 A206035 * A206037 A206038 A206039


KEYWORD

nonn


AUTHOR

Jaroslav Krizek, Feb 03 2012


STATUS

approved



