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%I #20 Jun 11 2018 05:54:11
%S 188,1155,2540,5831,6560,8449,9074,11235,11448,25885,32318,54144,
%T 56168,61016,63535,76879,91874,99980,118335,119144,123100,127007,
%U 146015,153759,219699,227528,234255,243048,280370,404319,405768,408968,431648,463346,504007
%N Composite numbers k such that (k+1)*sigma(k) is a perfect square.
%C Trivially if p is prime then (p+1)*sigma(p) = (p+1)^2.
%H Donovan Johnson, <a href="/A073586/b073586.txt">Table of n, a(n) for n = 1..1000</a>
%e 1156*sigma(1155) = 1632^2, hence 1155 is in the sequence.
%t Select[Range[505000], ! PrimeQ[#] && IntegerQ[Sqrt[(# + 1)*DivisorSigma[1, #]]] &] (* _Jayanta Basu_, Jul 02 2013 *)
%o (PARI) isA073586(n)=(!isprime(n))&&issquare((n+1)*sigma(n)) \\ _Michael B. Porter_, Apr 05 2010
%Y Cf. A069953.
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Aug 28 2002
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