OFFSET
0,3
COMMENTS
All terms seem to be odd.
EXAMPLE
E.g.f.: A(x) = 1 + x^2/2! + 3*x^4/4! + 31*x^6/6! + 553*x^8/8! + 18961*x^10/10! + 874203*x^12/12! + 62142991*x^14/14! + 5423159953*x^16/16! + 655008561121*x^18/18! +...
where A(x)^2 = cosh(x) / cos(x):
A(x)^2 = 1 + 2*x^2 + 12*x^4 + 152*x^6 + 3472*x^8 + 126752*x^10 + 6781632*x^12 + 500231552*x^14 +...+ A000795(n)*x^(2*n)/(2*n)! +...
PROG
(PARI) {a(n) = (2*n)! * polcoeff( sqrt( cosh(x + x*O(x^(2*n))) / cos(x + x*O(x^(2*n))) ) , 2*n)}
for(n=0, 20, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, May 21 2016
STATUS
approved