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 A212310 #19 May 01 2021 15:57:19 %S A212310 0,1,2,6,24,120,720,5040,40320,100736,483072,2168064,9239552,53005312, %T A212310 205203456,930568192,2004189184,12596379648,54936141824,81714020352, %U A212310 534768779264,1334539714560,2971594653696,68346677035008,232945365286912,1038559528091648,2232749779845120 %N A212310 a(n) = n! mod 4^n. %H A212310 Seiichi Manyama, <a href="/A212310/b212310.txt">Table of n, a(n) for n = 0..1000</a> %o A212310 (Python) %o A212310 import math %o A212310 print([math.factorial(n)%(4**n) for n in range(99)]) %o A212310 (PARI) a(n) = n! % 4^n; \\ _Michel Marcus_, Jan 22 2021 %Y A212310 Cf. A000142, A000302, A068496, A212309. %K A212310 nonn,easy %O A212310 0,3 %A A212310 _Alex Ratushnyak_, Oct 24 2013