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

Author

Giovanni Resta, Feb 13 2006

Keywords

• nonn

Examples

			6111+sigma(6111)+sigma(sigma(6111))=T(286).
		

Crossrefs

Cf. A116012, A116013, A116014.

Programs

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 *)