The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #4 Feb 24 2012 12:51:07
%S 1,-1,9,-225,6993,-592545,38019993,-7568120833,704958936737,
%T -307874830583745,28902473366214185,-31727751790145150113,
%U 1072204316646061940721,-7192967681050724533661025
%N sech(arctanh(x)*cos(x))=1-1/2!*x^2+9/4!*x^4-225/6!*x^6+6993/8!*x^8...
%K sign
%O 0,3
%A Patrick Demichel (patrick.demichel(AT)hp.com)