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 A272656 #18 Aug 03 2022 17:46:54
%S A272656 1,1,13,461,29093,2829325,392743957,73943424413,18176728317413,
%T A272656 5661698774848621,2181096921557783605,1018705098450570562877,
%U A272656 567347013156626397484421,371514945708955154128328461,282629242654284555347577144277,247210800978211588125067686948317
%N A272656 Bisection of A003319: a(n) = A003319(2n).
%H A272656 Michael De Vlieger, <a href="/A272656/b272656.txt">Table of n, a(n) for n = 0..224</a> (a(n) for n = 1..200 from Vincenzo Librandi)
%t A272656 (* b = A003319 *) b[n_] := b[n] = n! - Sum[k!*b[n-k], {k, 1, n-1} ]; a[n_] := b[2 n]; Table[a[n], {n, 0, 15}] (* _Jean-François Alcover_, Feb 18 2018 *)
%Y A272656 Cf. A003319, A272657.
%K A272656 nonn
%O A272656 0,3
%A A272656 _N. J. A. Sloane_, May 15 2016
%E A272656 a(0) = 1 set by _Peter Luschny_, Aug 03 2022