This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A380656 #19 Feb 05 2025 21:59:33 %S A380656 0,1,0,0,0,2,0,0,0,1,0,1,0,1,1,0,0,1,0,1,0,1,0,1,0,1,0,1,0,2,0,0,0,1, %T A380656 1,0,0,1,0,0,0,3,0,1,0,1,0,0,0,1,0,1,0,1,0,1,0,1,0,2,0,1,0,0,0,4,0,0, %U A380656 0,4,0,1,0,1,0,1,0,2,0,0,0,1,0,0,0,1,0,0,0,2,1,1,0,1,0,1,0,1,0,0 %N A380656 a(n) is the number of divisors d such that -d^n mod n = d. %t A380656 a[n_] := DivisorSum[n, 1 &, Mod[-PowerMod[#, n, n], n] == # &]; Array[a, 100] (* _Amiram Eldar_, Feb 04 2025 *) %o A380656 (Magma) [#[d: d in Divisors(n) | -d^n mod n eq d]: n in [1..100]]; %Y A380656 Cf. A000005, A371883. %K A380656 nonn %O A380656 1,6 %A A380656 _Juri-Stepan Gerasimov_, Feb 03 2025