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 A212309 #26 May 22 2021 04:34:37
%S A212309 0,1,2,6,24,120,720,666,954,8586,26811,58725,173259,1189485,3898206,
%T A212309 1077462,17239392,34789338,238787595,275338926,2019994119,578463687,
%U A212309 2265847911,52114501953,121029900948,201452158890,1848601693368,4158660811014,2058540433587,36820880119062
%N A212309 a(n) = n! mod 3^n.
%H A212309 Seiichi Manyama, <a href="/A212309/b212309.txt">Table of n, a(n) for n = 0..1000</a>
%t A212309 Table[Mod[n!,3^n],{n,0,30}] (* _Harvey P. Dale_, Apr 01 2018 *)
%o A212309 (Python)
%o A212309 import math
%o A212309 print([math.factorial(n)%(3**n) for n in range(99)])
%o A212309 (PARI) a(n) = n! % 3^n; \\ _Michel Marcus_, Jan 22 2021
%Y A212309 Cf. A000142, A000244, A068496, A212310.
%K A212309 nonn,easy
%O A212309 0,3
%A A212309 _Alex Ratushnyak_, Oct 24 2013