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 A381274 #9 Feb 19 2025 03:36:34
%S A381274 1,1,1,28,109,676,10261,65584,881497,11930896,122708521,2186539840,
%T A381274 30542901445,477545743936,9168255077437,149358238356736,
%U A381274 3043023842477233,61000460650291456,1225825910880514129,28395625697194028032,621110654837608378141,14936817377079335166976
%N A381274 Expansion of e.g.f. exp(x * cosh(3*x)).
%C A381274 As stated in the comment of A185951, A185951(n,0) = 0^n.
%F A381274 a(0) = 1; a(n) = Sum_{k=0..floor((n-1)/2)} 9^k * (2*k+1) * binomial(n-1,2*k) * a(n-2*k-1).
%F A381274 a(n) = Sum_{k=0..n} 3^(n-k) * A185951(n,k).
%o A381274 (PARI) a185951(n, k) = binomial(n, k)/2^k*sum(j=0, k, (2*j-k)^(n-k)*binomial(k, j));
%o A381274 a(n) = sum(k=0, n, 3^(n-k)*a185951(n, k));
%Y A381274 Cf. A003727, A381273.
%Y A381274 Cf. A185951.
%K A381274 nonn
%O A381274 0,4
%A A381274 _Seiichi Manyama_, Feb 18 2025