%I #6 Feb 24 2012 12:50:50
%S 2,0,40,-2688,210208,-13038080,2241915520,-589026013184,
%T 146361182839296,-42690102749216768,18963982821764573184,
%U -10109322351828827471872,5702647873782168851521536
%N arcsinh(arctan(x)*tan(x))=2/2!*x^2+40/6!*x^6-2688/8!*x^8+210208/10!*x^10...
%F a(n) = (2n)! [ x^(2n) ] arcsinh(arctan(x)*tan(x)).
%K sign
%O 1,1
%A Patrick Demichel (patrick.demichel(AT)hp.com)