OFFSET
2,1
COMMENTS
The number of faces is 2. - Andrew Howroyd, Apr 05 2021
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..1000
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
From Colin Barker, Apr 08 2013: (Start)
a(n) = (n*(12-28*n-45*n^2+20*n^3+33*n^4+8*n^5))/360.
G.f.: -x^2*(x^2 + 11*x + 4) / (x-1)^7. (End)
a(n) = binomial(n+2,4)*(8*n^2 + 17*n - 6)/15. - Andrew Howroyd, Apr 05 2021
PROG
(PARI) a(n) = {binomial(n+2, 4)*(8*n^2 + 17*n - 6)/15} \\ Andrew Howroyd, Apr 05 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Title improved by Sean A. Irvine, Apr 03 2017
Terms a(11) and beyond from Andrew Howroyd, Apr 05 2021
STATUS
approved