%I #7 Aug 15 2015 15:16:56
%S 1,6,24,5040,72576,39916800,95800320,1307674368000,4184557977600,
%T 121645100408832000,2043637686868377600,25852016738884976640000,
%U 238634000666630553600000,10888869450418352160768000000
%N Reduced denominators in the Maclaurin series for the Gudermannian.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Gudermannian.html">Gudermannian</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/InverseGudermannian.html">Inverse Gudermannian</a>
%e x - x^3/6 + x^5/24 - (61*x^7)/5040 + (277*x^9)/72576 - ...
%t gd[x_] := 2*ArcTan[(E^x - 1)/(E^x + 1)]; CoefficientList[ Series[gd[x], {x, 0, 28}]/x , x^2] // Denominator (* _Jean-François Alcover_, Nov 09 2012 *)
%Y Cf. A091912.
%K nonn
%O 1,2
%A _Eric W. Weisstein_, Jan 12 2008