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 A009379 #18 Dec 21 2017 17:28:06
%S A009379 0,2,-4,96,-2080,125440,-8629248,996007936,-140162633728,
%T A009379 27058965184512,-6350990843576320,1866805063173799936,
%U A009379 -653569786506324738048,273136898848234632380416,-133034893921204302732328960
%N A009379 Expansion of log(1+tan(x)*x).
%F A009379 a(n) ~ (2*n)! * (-1)^(n+1) / (n * r^(2*n)), where r = 1.1996786402577338339163698486411419442614587884... (see A085984) is the root of the equation r*tanh(r) = 1. - _Vaclav Kotesovec_, Jan 23 2015
%t A009379 Log[ 1+Tan[ x ]*x ] (* Even Part *)
%t A009379 nn = 20; Table[(CoefficientList[Series[Log[1 + x*Tan[x]], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* _Vaclav Kotesovec_, Jan 23 2015 *)
%Y A009379 Cf. A009399, A085984.
%K A009379 sign
%O A009379 0,2
%A A009379 _R. H. Hardin_
%E A009379 Extended with signs by _Olivier Gérard_, Mar 15 1997