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 A272657 #11 Aug 03 2022 17:46:31
%S A272657 1,3,71,3447,273343,31998903,5201061455,1123596277863,311951144828863,
%T A272657 108355864447215063,46066653228356851631,23539631662517304379719,
%U A272657 14238556471214701698866335,10063612905845566536549621687,8219089293266835899526592972943,7682002790499533568011331441585447
%N A272657 Bisection of A003319: a(n) = A003319(2n+1).
%H A272657 Vincenzo Librandi, <a href="/A272657/b272657.txt">Table of n, a(n) for n = 0..200</a>
%t A272657 (* b = A003319 *) b[0] = 0; b[n_] := b[n] = n! - Sum[k!*b[n-k], {k, 1, n-1} ]; a[n_] := b[2n + 1]; Table[a[n], {n, 0, 15}] (* _Jean-François Alcover_, Feb 18 2018 *)
%Y A272657 Cf. A003319, A272656.
%K A272657 nonn
%O A272657 0,2
%A A272657 _N. J. A. Sloane_, May 15 2016