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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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: A284302 A284350 A107014 * A132628 A288928 A039509 Adjacent sequences:  A206033 A206034 A206035 * A206037 A206038 A206039 KEYWORD nonn AUTHOR Jaroslav Krizek, Feb 03 2012 STATUS approved

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Last modified February 18 02:57 EST 2020. Contains 332006 sequences. (Running on oeis4.)