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 A384258 #9 May 23 2025 10:15:17
%S A384258 1,2,21,384,9945,332640,13627845,660602880,36974963025,2346549004800,
%T A384258 166490632833525,13059009124761600,1122040194333683625,
%U A384258 104802322548059136000,10572978481108199281125,1145749403453003661312000,132730561036298082383150625,16369108295524571830763520000
%N A384258 a(n) = Product_{k=0..n-1} (n+4*k+1).
%F A384258 a(n) = 4^n * RisingFactorial((n+1)/4,n).
%F A384258 a(n) = n! * [x^n] 1/(1 - 4*x)^((n+1)/4).
%o A384258 (PARI) a(n) = prod(k=0, n-1, n+4*k+1);
%o A384258 (Sage)
%o A384258 def a(n): return 4^n*rising_factorial((n+1)/4, n)
%Y A384258 Cf. A303487, A384259.
%K A384258 nonn,easy
%O A384258 0,2
%A A384258 _Seiichi Manyama_, May 23 2025