A073586 Composite numbers k such that (k+1)*sigma(k) is a perfect square.

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

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