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 A357719 #14 Jul 23 2025 09:08:14
%S A357719 1,0,-4,12,-28,40,200,-3360,35680,-357120,3644800,-38896000,437756800,
%T A357719 -5206406400,65372153600,-864339840000,11991424640000,
%U A357719 -173800340480000,2617640829440000,-40693929269760000,647089190924800000,-10383194262604800000
%N A357719 Expansion of e.g.f. cos( 2 * log(1+x) ).
%H A357719 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PochhammerSymbol.html">Pochhammer Symbol</a>.
%F A357719 a(n) = Sum_{k=0..floor(n/2)} (-4)^k * Stirling1(n,2*k).
%F A357719 a(n) = (-1)^n * ( (2 * i)_n + (-2 * i)_n )/2, where (x)_n is the Pochhammer symbol and i is the imaginary unit.
%F A357719 a(0) = 1, a(1) = 0; a(n) = -(2*n-3) * a(n-1) - (n^2-4*n+8) * a(n-2).
%o A357719 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(cos(2*log(1+x))))
%o A357719 (PARI) a(n) = sum(k=0, n\2, (-4)^k*stirling(n, 2*k, 1));
%o A357719 (PARI) a(n) = (-1)^n*(prod(k=0, n-1, 2*I+k)+prod(k=0, n-1, -2*I+k))/2;
%o A357719 (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+8)*v[i-1]); v;
%Y A357719 Column k=4 of A357720.
%Y A357719 Cf. A357711, A357727.
%K A357719 sign
%O A357719 0,3
%A A357719 _Seiichi Manyama_, Oct 10 2022