A114069 sigma(n) + n is a square.

33, 90, 385, 420, 649, 900, 1441, 1464, 1480, 1729, 2025, 2616, 3168, 3588, 3984, 4005, 4873, 5049, 5185, 6225, 7153, 7585, 8740, 9060, 10285, 11080, 12280, 12609, 13914, 14809, 15136, 16065, 16345, 17017, 17353, 17809, 18073, 18625, 19098

Offset: 1

Author

Giovanni Resta, Feb 13 2006

Keywords

• nonn

Examples

			sigma(33) + 33 = 81 = 9^2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A155085.

Programs

Mathematica

Select[Range[20000],IntegerQ[Sqrt[DivisorSigma[1,#]+#]]&] (* Harvey P. Dale, May 09 2011 *)

PARI

isok(n) = issquare (n+sigma(n)); \\ Michel Marcus, Aug 13 2019