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 A009281 #24 Jan 05 2024 07:56:36
%S A009281 1,1,2,1,7,-19,136,-923,7421,-66743,667486,-7342279,88107427,
%T A009281 -1145396459,16035550532,-240533257859,3848532125881,-65425046139823,
%U A009281 1177650830516986,-22375365779822543,447507315596451071,-9397653627525472259,206748379805560389952,-4755212735527888968619,114125105652669335247157
%N A009281 Expansion of e.g.f. exp(x)*cosh(log(1+x)).
%F A009281 a(n) ~ n! * (-1)^n / (2*exp(1)). - _Vaclav Kotesovec_, Jan 22 2015
%F A009281 a(n) = ((-1)^n * A000387(n)) + 1. - _Christian Krause_, Jan 05 2024
%t A009281 With[{nn=20},CoefficientList[Series[Exp[x]*Cosh[Log[1+x]],{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Sep 02 2016 *)
%t A009281 CoefficientList[Series[(E^x*(1 + (1 + x)^2))/(2*(1 + x)), {x, 0, 20}], x] * Range[0, 20]! (* _Vaclav Kotesovec_, Jan 22 2015 *)
%o A009281 (PARI) my(x='x+O('x^66)); Vec(serlaplace(exp(x)*cosh(log(1+x)))) \\ _Joerg Arndt_, Jan 05 2024
%Y A009281 Cf. A000387.
%K A009281 sign,easy
%O A009281 0,3
%A A009281 _R. H. Hardin_
%E A009281 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009281 Prior Mathematica program replaced by _Harvey P. Dale_, Sep 02 2016