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 A357711 #17 Jul 23 2025 09:08:10
%S A357711 1,0,4,12,60,360,2520,20160,181440,1814400,19958400,239500800,
%T A357711 3113510400,43589145600,653837184000,10461394944000,177843714048000,
%U A357711 3201186852864000,60822550204416000,1216451004088320000,25545471085854720000,562000363888803840000
%N A357711 Expansion of e.g.f. cosh( 2 * log(1-x) ).
%H A357711 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PochhammerSymbol.html">Pochhammer Symbol</a>.
%F A357711 a(n) = Sum_{k=0..floor(n/2)} 4^k * |Stirling1(n,2*k)|.
%F A357711 a(n) = ( (2)_n + (-2)_n )/2, where (x)_n is the Pochhammer symbol.
%F A357711 a(n) = (n+1)!/2 for n > 2.
%F A357711 a(0) = 1, a(1) = 0; a(n) = (2*n-3) * a(n-1) - (n^2-4*n) * a(n-2).
%o A357711 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(cosh(2*log(1-x))))
%o A357711 (PARI) a(n) = sum(k=0, n\2, 4^k*abs(stirling(n, 2*k, 1)));
%o A357711 (PARI) a(n) = (prod(k=0, n-1, 2+k)+prod(k=0, n-1, -2+k))/2;
%o A357711 (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=2, n, v[i+1]=(2*i-3)*v[i]-(i^2-4*i)*v[i-1]); v;
%Y A357711 Column k=4 of A357712.
%Y A357711 Cf. A065143.
%K A357711 nonn
%O A357711 0,3
%A A357711 _Seiichi Manyama_, Oct 10 2022