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 A381208 #10 Feb 17 2025 08:18:19
%S A381208 1,2,6,18,48,10,-1440,-17654,-153216,-1003950,-2787840,58057538,
%T A381208 1483941888,22381115354,245730121728,1455189928890,-18135147970560,
%U A381208 -856283065534046,-19218870434267136,-306007541260257422,-2933654664287354880,20552099782407258282,1938717354581701951488
%N A381208 Expansion of e.g.f. 1/(1 - x*cos(x))^2.
%C A381208 As stated in the comment of A185951, A185951(n,0) = 0^n.
%F A381208 a(n) = Sum_{k=0..n} (k+1)! * i^(n-k) * A185951(n,k), where i is the imaginary unit.
%o A381208 (PARI) a185951(n, k) = binomial(n, k)/2^k*sum(j=0, k, (2*j-k)^(n-k)*binomial(k, j));
%o A381208 a(n) = sum(k=0, n, (k+1)!*I^(n-k)*a185951(n, k));
%Y A381208 Cf. A352252, A381209.
%Y A381208 Cf. A185951.
%K A381208 sign
%O A381208 0,2
%A A381208 _Seiichi Manyama_, Feb 17 2025