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 A385392 #23 Aug 22 2025 02:16:24 %S A385392 1,2,1,1,1,3,1,1,1,2,1,1,1,2,2,1,1,2,1,2,1,2,1,2,1,2,1,1,1,3,1,1,1,2, %T A385392 2,1,1,2,1,1,1,4,1,1,1,2,1,1,1,2,1,2,1,2,1,1,1,2,1,2,1,2,1,1,1,3,1,1, %U A385392 1,5,1,2,1,2,1,1,1,3,1,1,1,2,1,1,1,2,1,1,1,2,2,1,1,2,1,2,1,2,1,1 %N A385392 The number of divisors d of n such that -(d^d) == d (mod n). %p A385392 a:= n-> add(`if`(d&^d+d mod n=0, 1, 0), d=numtheory[divisors](n)): %p A385392 seq(a(n), n=1..100); # _Alois P. Heinz_, Jun 27 2025 %t A385392 a[n_] := DivisorSum[n, 1 &, PowerMod[#, #, n] == n-# &]; Array[a, 100] (* _Amiram Eldar_, Jun 27 2025 *) %o A385392 (PARI) a(n) = sumdiv(n, d, -Mod(d, n)^d == d); \\ _Michel Marcus_, Jun 27 2025 %o A385392 (Magma) [1+#[d: d in [1..n-1] | n mod d eq 0 and Modexp(d, d, n) eq (n-d)]: n in [1..100]]; // _Juri-Stepan Gerasimov_, Jun 28 2025 %Y A385392 Cf. A032741, A065295, A384237, A384781, A384854, A385103. %K A385392 nonn,changed %O A385392 1,2 %A A385392 _Juri-Stepan Gerasimov_, Jun 27 2025