A006434 Number of tree-rooted toroidal maps with 2 faces and n vertices and without separating loops or isthmuses.

4, 120, 1230, 7424, 32424, 113584, 338742, 893220, 2136618, 4721728, 9770904

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• more

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• 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.

Crossrefs

Cf. A006435, A006436, A006439.

Formula

Empirical g.f.: 2*x*(x^6+8*x^5-13*x^4+22*x^3+105*x^2+40*x+2) / (x-1)^10. - Colin Barker, Apr 09 2013

Extensions

Name clarified by Andrew Howroyd, Apr 04 2021