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 A116015 n+sigma(n)+sigma(sigma(n)) is a triangular number. 4
 1, 9, 43, 109, 119, 161, 175, 192, 232, 490, 843, 1050, 1162, 1242, 1635, 1959, 2113, 2859, 2935, 3008, 3174, 3469, 3717, 4165, 4173, 4761, 4839, 4876, 5200, 6111, 6423, 6468, 8008, 8480, 9064, 9523, 9603, 11143, 11197, 11353, 11557, 11773 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Table of n, a(n) for n=1..42. EXAMPLE 6111+sigma(6111)+sigma(sigma(6111))=T(286). MATHEMATICA triangularQ[n_] := IntegerQ[Sqrt[8n + 1]]; Reap[For[n = 1, n < 12000, n++, s = DivisorSigma[1, n]; If[triangularQ[n + s + DivisorSigma[1, s]], Sow[n]]]][[2, 1]] (* Jean-François Alcover, Oct 15 2013 *) CROSSREFS Cf. A116012, A116013, A116014. Sequence in context: A224836 A195975 A185918 * A332373 A181945 A244869 Adjacent sequences: A116012 A116013 A116014 * A116016 A116017 A116018 KEYWORD nonn AUTHOR Giovanni Resta, Feb 13 2006 STATUS approved

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Last modified August 7 17:47 EDT 2024. Contains 375017 sequences. (Running on oeis4.)