A067719 Numbers k such that sigma(k^2 + 1) == 0 (mod k).

1, 2, 3, 9, 12, 21, 33, 72, 93, 196, 228, 252, 360, 475, 850, 1458, 1725, 1752, 2100, 2241, 2584, 3007, 3404, 4347, 4743, 5544, 5720, 6555, 6600, 9909, 10512, 14175, 15507, 16680, 19404, 26460, 29008, 29484, 36003, 36400, 37107, 46728, 88209, 88641, 89424, 94770

Offset: 1

Author

Benoit Cloitre, Feb 05 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..250 (terms 1..100 from Harvey P. Dale)

Crossrefs

Cf. A000203, A002522, A193433.

Programs

Maple

q:= n-> is(irem(numtheory[sigma](n^2+1), n)=0):
select(q, [$1..100000])[];  # Alois P. Heinz, Jan 26 2023

Mathematica

Select[Range[50000],Divisible[DivisorSigma[1,#^2+1],#]&] (* Harvey P. Dale, Nov 04 2011 *)