OFFSET
1,1
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1273 terms from Amiram Eldar).
MATHEMATICA
Select[Range[10^5], IntegerQ[Sqrt[ # + 1]] && IntegerQ[Sqrt[DivisorSigma[1, # ] + 1]] &]
PROG
(PARI) upto(n) = {my(res = List()); for(i = 2, sqrtint(n + 1), if(issquare(sigma(i^2 - 1) + 1), listput(res, i^2 - 1))); res} \\ David A. Corneth, Aug 14 2019
(Magma) [n:n in [m*m-1:m in [2..700]]| IsSquare(SumOfDivisors(n)+1)]; // Marius A. Burtea, Aug 14 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Joseph L. Pe, Jan 17 2004
EXTENSIONS
More terms from Amiram Eldar, Aug 14 2019
STATUS
approved