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 A180491 #10 Nov 02 2024 04:24:59 %S A180491 1,1,1,0,2,0,6,0,0,0,720,0,2160,0,0,0,2419200,0,65318400,0,0,0, %T A180491 754427520000,0,0,0,0,0,32953394073600000,0,311409573995520000,0,0,0, %U A180491 0,0,37269497815783833600000,0,0,0,7890485108998805913600000000,0 %N A180491 Product of remainders of n mod k, for k = 2,3,4,...,n-1. %C A180491 a(n) is zero where n is composite and is trivially less than or equal to n! when n is prime or 1. %C A180491 a(n)=0 iff n is composite. See A180492. - _Robert G. Wilson v_, Sep 09 2010 %F A180491 a(n) = A080339(n)*A173392(n). - _Ridouane Oudra_, Nov 01 2024 %e A180491 a(7) = (7 mod 2) * (7 mod 3) * (7 mod 4) * (7 mod 5) * (7 mod 6) = 1 * 1 * 3 * 2 * 1 = 6. %p A180491 a:=proc(n) if n=1 then 1; elif isprime(n)=true then mul(n mod i, i=2..n-1); else 0; fi: end: seq(a(n), n=1..60); # _Ridouane Oudra_, Nov 01 2024 %t A180491 f[n_] := Times @@ Mod[n, Range[2, n - 1]]; Array[f, 42] (* _Robert G. Wilson v_, Sep 09 2010 *) %Y A180491 Cf. A034386, A000142, A004125, A180492, A180493. %Y A180491 Cf. A080339, A173392. %K A180491 nonn %O A180491 1,5 %A A180491 _Carl R. White_, Sep 08 2010