OFFSET
2,2
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Andrew Howroyd, Table of n, a(n) for n = 2..500
T. R. S. Walsh and A. B. Lehman, Counting rooted maps by genus. III: Nonseparable maps, J. Combinatorial Theory Ser. B 18 (1975), 222-259.
FORMULA
G.f.: x^2*(1 + 2*g - 4*g^2)/((1 - g)^4*(1 - 2*g)^5)) where g/x is the g.f. of A000108.
PROG
(PARI) seq(n)={my(g=x*(1-sqrt(1-4*x + O(x^n)))/(2*x)); Vec((1 + 2*g - 4*g^2)/((1 - g)^4*(1 - 2*g)^5))} \\ Andrew Howroyd, Apr 06 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(14) and a(15) from Sean A. Irvine, Apr 05 2017
Terms a(16) and beyond from Andrew Howroyd, Apr 02 2021
STATUS
approved