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

1,2

Links

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

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 *)

Crossrefs

Cf. A000203, A002522, A193433.

Sequence in context: A168080 A048084 A350439 * A057017 A330298 A330242

Adjacent sequences: A067716 A067717 A067718 * A067720 A067721 A067722

Keyword

nonn

Author

Benoit Cloitre, Feb 05 2002

Status

approved