%I #4 Feb 24 2012 12:50:42
%S 1,1,21,1101,107209,16711481,3810146205,1195529025861,494050576455185,
%T 260086639760540401,169928807728242392485,134924876918419856397501,
%U 127963083862513681084495321
%N sec(tan(arctanh(x)))=1+1/2!*x^2+21/4!*x^4+1101/6!*x^6+107209/8!*x^8...
%K nonn
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)