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 A383996 #16 May 23 2025 02:00:42
%S A383996 1,1,-4,15,0,-1155,20160,-208845,0,68139225,-2075673600,34976316375,0,
%T A383996 -25949801752875,1126343522304000,-26264240610733125,0,
%U A383996 34770736214117528625,-1958486116582195200000,58318039100493206409375,0,-120842042784862988395681875,8366746697372733839769600000
%N A383996 a(n) = Product_{k=0..n-1} (n-4*k).
%F A383996 a(n) = 4^n * FallingFactorial(n/4,n).
%F A383996 a(n) = n! * [x^n] (1 + 4*x)^(n/4).
%F A383996 a(4*n) = 0 for n > 0.
%o A383996 (PARI) a(n) = prod(k=0, n-1, n-4*k);
%o A383996 (Sage)
%o A383996 def a(n): return 4^n*falling_factorial(n/4, n)
%Y A383996 Column k=4 of A384216.
%Y A383996 Cf. A303487.
%K A383996 sign,easy
%O A383996 0,3
%A A383996 _Seiichi Manyama_, May 22 2025