OFFSET
1,3
FORMULA
E.g.f.: log(sech(x)+arctanh(x)).
EXAMPLE
x - 2/2!*x^2 + 7/3!*x^3 - 24/4!*x^4 + 173/5!*x^5 ...
PROG
(PARI) a(n)=local(y); if(n<0, 0, y=x+x*O(x^n); n!*polcoeff(log(1/cosh(y)+atanh(y)), n))
CROSSREFS
KEYWORD
sign
AUTHOR
Patrick Demichel (patrick.demichel(AT)hp.com)
EXTENSIONS
a(0)=0 inserted and title improved by Sean A. Irvine, Aug 01 2018
STATUS
approved