OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
sigma(33) + 33 = 81 = 9^2.
MATHEMATICA
Select[Range[20000], IntegerQ[Sqrt[DivisorSigma[1, #]+#]]&] (* Harvey P. Dale, May 09 2011 *)
PROG
(PARI) isok(n) = issquare (n+sigma(n)); \\ Michel Marcus, Aug 13 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved