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 A073586 Composite numbers k such that (k+1)*sigma(k) is a perfect square. 1
 188, 1155, 2540, 5831, 6560, 8449, 9074, 11235, 11448, 25885, 32318, 54144, 56168, 61016, 63535, 76879, 91874, 99980, 118335, 119144, 123100, 127007, 146015, 153759, 219699, 227528, 234255, 243048, 280370, 404319, 405768, 408968, 431648, 463346, 504007 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Trivially if p is prime then (p+1)*sigma(p) = (p+1)^2. LINKS Donovan Johnson, Table of n, a(n) for n = 1..1000 EXAMPLE 1156*sigma(1155) = 1632^2, hence 1155 is in the sequence. MATHEMATICA Select[Range[505000], ! PrimeQ[#] && IntegerQ[Sqrt[(# + 1)*DivisorSigma[1, #]]] &] (* Jayanta Basu, Jul 02 2013 *) PROG (PARI) isA073586(n)=(!isprime(n))&&issquare((n+1)*sigma(n)) \\ Michael B. Porter, Apr 05 2010 CROSSREFS Cf. A069953. Sequence in context: A335592 A233786 A233961 * A064115 A185241 A211818 Adjacent sequences:  A073583 A073584 A073585 * A073587 A073588 A073589 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Aug 28 2002 STATUS approved

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Last modified July 30 10:27 EDT 2021. Contains 346359 sequences. (Running on oeis4.)