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 A045746 Numbers n such that the sum of the divisors of n is a triangular number. 9
 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 (list; graph; refs; listen; history; text; internal format)
 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 A004711 A291922 Adjacent sequences:  A045743 A045744 A045745 * A045747 A045748 A045749 KEYWORD nonn AUTHOR STATUS approved

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Last modified October 29 13:26 EDT 2020. Contains 338066 sequences. (Running on oeis4.)