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 A381273 #11 Feb 19 2025 03:40:32
%S A381273 1,1,1,13,49,201,2161,12629,102817,1118161,9109921,105660765,
%T A381273 1223720785,13461561881,186666204817,2406325357861,33607592404033,
%U A381273 516511765519521,7658010172957249,126206019752173997,2115466479287184241,36218229615683409001,666810643855970901937
%N A381273 Expansion of e.g.f. exp(x * cosh(2*x)).
%C A381273 As stated in the comment of A185951, A185951(n,0) = 0^n.
%F A381273 a(0) = 1; a(n) = Sum_{k=0..floor((n-1)/2)} 4^k * (2*k+1) * binomial(n-1,2*k) * a(n-2*k-1).
%F A381273 a(n) = Sum_{k=0..n} 2^(n-k) * A185951(n,k).
%o A381273 (PARI) a185951(n, k) = binomial(n, k)/2^k*sum(j=0, k, (2*j-k)^(n-k)*binomial(k, j));
%o A381273 a(n) = sum(k=0, n, 2^(n-k)*a185951(n, k));
%Y A381273 Cf. A003727, A381274.
%Y A381273 Cf. A185951.
%K A381273 sign
%O A381273 0,4
%A A381273 _Seiichi Manyama_, Feb 18 2025