A012840 exp(sec(x)*arctanh(x))=1+x+1/2!*x^2+6/3!*x^3+21/4!*x^4+120/5!*x^5...
1, 1, 1, 6, 21, 120, 765, 5376, 46473, 415104, 4371225, 48143744, 594635613, 7784817664, 110691178325, 1673986906112, 27018807872657, 462531126525952, 8370279766396593, 159859054841331712
Offset: 0