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 A383997 #14 May 23 2025 02:00:45
%S A383997 1,1,-6,42,-264,0,57456,-1808352,40715136,-643458816,0,583285038336,
%T A383997 -32763345398784,1237080874917888,-31193431756591104,0,
%U A383997 64105508174249558016,-5177532237241354518528,274167069135623993032704,-9487174826303791319678976,0
%N A383997 a(n) = Product_{k=0..n-1} (n-5*k).
%F A383997 a(n) = 5^n * FallingFactorial(n/5,n).
%F A383997 a(n) = n! * [x^n] (1 + 5*x)^(n/5).
%F A383997 a(5*n) = 0 for n > 0.
%o A383997 (PARI) a(n) = prod(k=0, n-1, n-5*k);
%o A383997 (Sage)
%o A383997 def a(n): return 5^n*falling_factorial(n/5, n)
%Y A383997 Column k=5 of A384216.
%Y A383997 Cf. A303488.
%K A383997 sign,easy
%O A383997 0,3
%A A383997 _Seiichi Manyama_, May 22 2025