OFFSET
0,6
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..500
Wikipedia, Cactus graph.
FORMULA
G.f. 1 + A(x) where A(x) satisfies A(x) = x^2*(x - A(x)^2)/(x^2 - x*A(x)^2 - A(x)^4).
PROG
(PARI) seq(n)={my(g=1+O(x)); for(n=1, n\2, g=1/(1 - x^2*g^4/(1 - x*g^2))); Vec(1 + x*g + O(x*x^n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Mar 08 2023
STATUS
approved