A380833 a(n) is the number of divisors d of n satisfying (-d)^n mod n = d.

0, 1, 0, 1, 0, 2, 0, 1, 0, 2, 0, 2, 0, 2, 1, 1, 0, 2, 0, 2, 0, 2, 0, 1, 0, 2, 0, 2, 0, 4, 0, 1, 0, 2, 1, 2, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 1, 0, 2, 0, 1, 0, 4, 0, 2, 0, 2, 0, 2, 0, 2, 0, 1, 0, 3, 0, 2, 0, 2, 0, 3, 0, 2, 0, 1, 0, 3, 1, 1, 0, 2, 0, 1, 0, 2, 0, 2

Offset: 1

Author

Juri-Stepan Gerasimov, Feb 06 2025

Keywords

• nonn

Crossrefs

Cf. A000005, A371883, A380656.

Programs

Magma

[#[d: d in Divisors(n) | (-d)^n mod n eq d]: n in [1..100]];

Mathematica

a[n_] := DivisorSum[n, 1 &, PowerMod[-#, n, n] == # &]; Array[a, 100] (* Amiram Eldar, Feb 06 2025 *)