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 A384854 #22 Aug 22 2025 17:38:39 %S A384854 1,2,1,1,1,2,1,1,1,2,1,2,1,2,2,1,1,2,1,1,1,2,1,1,1,2,1,2,1,5,1,1,1,2, %T A384854 2,2,1,2,1,1,1,2,1,1,1,2,1,2,1,2,1,1,1,2,1,2,1,2,1,1,1,2,1,1,1,3,1,1, %U A384854 1,3,1,1,1,2,1,1,1,2,1,2,1,2,1,3,1,2,1,1,1,3,2,1,1,2,1,1,1,2,1,1 %N A384854 The number of divisors d of n such that (-d)^d == d (mod n). %H A384854 Robert Israel, <a href="/A384854/b384854.txt">Table of n, a(n) for n = 1..10000</a> %F A384854 a(n) = 1 + number of proper divisors h of n such that (-h)^h = h (mod n). %p A384854 a:= n-> add(`if`((-d)&^d-d mod n=0, 1, 0), d=numtheory[divisors](n)): %p A384854 seq(a(n), n=1..100); # _Alois P. Heinz_, Jun 10 2025 %o A384854 (Magma) [1+#[s: s in [1..n-1] | n mod s eq 0 and Modexp((-s), s, n) eq s]: n in [1..100]]; %o A384854 (PARI) a(n) = sumdiv(n, d, Mod(-d, n)^d == d); \\ _Michel Marcus_, Jun 11 2025 %Y A384854 Cf. A000005, A032741, A065295, A384237, A384781. %K A384854 nonn,changed %O A384854 1,2 %A A384854 _Juri-Stepan Gerasimov_, Jun 10 2025