A013320 sec(exp(x)-cos(x))=1+1/2!*x^2+6/3!*x^3+21/4!*x^4+120/5!*x^5...

1, 0, 1, 6, 21, 120, 1077, 8918, 83097, 952560, 11790649, 156839430, 2318954253, 37207496040, 637980683277, 11745733936022, 231142374081009, 4825295491430880, 106636356923768497, 2489165244414184326