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 A009218 #23 Feb 14 2024 03:39:34
%S A009218 1,1,0,1,-2,6,-14,-20,876,-12572,157816,-1953324,24704560,-323390144,
%T A009218 4399642248,-62212681544,912281561296,-13817130664560,214872589110016,
%U A009218 -3401627908578992,54093656991247776,-844240783639323104
%N A009218 Expansion of e.g.f. exp(sinh(log(1+x))).
%F A009218 For n>2, a(n) = (-2*n+3)*a(n-1)-(n-3)*(n-1)*a(n-2)+(n-1)*(n-2)*a(n-3)/2. - _Tani Akinari_, Feb 13 2024
%t A009218 With[{m = 21}, Range[0, m]! * CoefficientList[Series[Exp[ Sinh[ Log[ 1+x ] ] ], {x, 0, m}], x]]
%o A009218 (Maxima) a[n]:=if n<3 then mod((n+1)^2,3) else (-2*n+3)*a[n-1]-(n-3)*(n-1)*a[n-2]+(n-1)*(n-2)*a[n-3]/2;
%o A009218 makelist(a[n],n,0,50); /* _Tani Akinari_, Feb 13 2024 */
%o A009218 (PARI) my(x='x+O('x^35)); Vec(serlaplace(exp(sinh(log(1+x))))) \\ _Joerg Arndt_, Feb 13 2024
%K A009218 sign,easy
%O A009218 0,5
%A A009218 _R. H. Hardin_
%E A009218 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009218 Name clarified by _Michel Marcus_, Feb 13 2024