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 A009398 #16 Jun 22 2015 22:30:13
%S A009398 0,2,-12,352,-16352,1382912,-172372992,30716649472,-7334631698432,
%T A009398 2270814362796032,-883463096359452672,422158497266733678592,
%U A009398 -243014206258719292915712,165880670114405086398513152
%N A009398 Expansion of log(1+tanh(x)*tan(x)).
%F A009398 a(n) ~ (2*n)! * (-1)^(n+1) * 2^(2*n) / (n * r^(2*n)), where r = 1.87510406871196116644530824107821416257011173353... (see A076417) is the root of the equation sin(r) = tanh(r). - _Vaclav Kotesovec_, Jan 24 2015
%t A009398 Log[ 1+Tanh[ x ]*Tan[ x ] ] (* Even Part *)
%t A009398 nn = 20; Table[(CoefficientList[Series[Log[1 + Tan[x]*Tanh[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* _Vaclav Kotesovec_, Jan 24 2015 *)
%Y A009398 Cf. A076417.
%K A009398 sign
%O A009398 0,2
%A A009398 _R. H. Hardin_
%E A009398 Extended with signs by _Olivier Gérard_, Mar 15 1997