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 A384256 #8 May 23 2025 10:15:26
%S A384256 1,2,18,280,6160,174960,6086080,250490240,11904278400,641472832000,
%T A384256 38645634227200,2573895458534400,187787322731008000,
%U A384256 14894027431162880000,1275931456704672768000,117412145664335441920000,11550258696757088788480000,1209613643310990696210432000
%N A384256 a(n) = Product_{k=0..n-1} (n+3*k+1).
%F A384256 a(n) = 3^n * RisingFactorial((n+1)/3,n).
%F A384256 a(n) = n! * [x^n] 1/(1 - 3*x)^((n+1)/3).
%o A384256 (PARI) a(n) = prod(k=0, n-1, n+3*k+1);
%o A384256 (Sage)
%o A384256 def a(n): return 3^n*rising_factorial((n+1)/3, n)
%Y A384256 Cf. A303486, A384257.
%K A384256 nonn,easy
%O A384256 0,2
%A A384256 _Seiichi Manyama_, May 23 2025