A116015 n+sigma(n)+sigma(sigma(n)) is a triangular number.

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

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