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%I #17 Jun 20 2021 02:29:00
%S 1,2,5,8,12,22,36,45,54,56,87,95,98,104,116,152,160,200,212,258,328,
%T 342,356,393,427,441,473,492,531,572,582,588,660,668,672,726,740,800,
%U 843,852,858,879,908,909,910,940,962,992
%N Numbers whose sum of divisors is a triangular number.
%H Charles R Greathouse IV, <a href="/A045746/b045746.txt">Table of n, a(n) for n = 1..10000</a>
%e sigma(8)=15 is a triangular number.
%t Select[Range[1000],IntegerQ[(Sqrt[1+8DivisorSigma[1,#]]-1)/2]&] (* _Harvey P. Dale_, Jul 14 2011 *)
%o (PARI) is(n)=ispolygonal(sigma(n),3) \\ _Charles R Greathouse IV_, Nov 10 2014
%Y Cf. A000203, A000217.
%K nonn
%O 1,2
%A _Felice Russo_
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