A045746 Numbers whose sum of divisors is a triangular number.

1, 2, 5, 8, 12, 22, 36, 45, 54, 56, 87, 95, 98, 104, 116, 152, 160, 200, 212, 258, 328, 342, 356, 393, 427, 441, 473, 492, 531, 572, 582, 588, 660, 668, 672, 726, 740, 800, 843, 852, 858, 879, 908, 909, 910, 940, 962, 992

Offset: 1

Author

Felice Russo

Keywords

• nonn

Examples

			sigma(8)=15 is a triangular number.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A000217.

Programs

Mathematica

Select[Range[1000],IntegerQ[(Sqrt[1+8DivisorSigma[1,#]]-1)/2]&] (* Harvey P. Dale, Jul 14 2011 *)

PARI

is(n)=ispolygonal(sigma(n),3) \\ Charles R Greathouse IV, Nov 10 2014