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

1,2

Links

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

Example

sigma(8)=15 is a triangular number.

Mathematica

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

Prog

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

Crossrefs

Cf. A000203, A000217.

Sequence in context: A049633 A066614 A305440 * A053614 A373640 A354007

Adjacent sequences: A045743 A045744 A045745 * A045747 A045748 A045749

Keyword

nonn

Author

Felice Russo

Status

approved