A002012 Almost trivalent maps. (Formerly M3643 N1481)

4, 32, 200, 1120, 5880, 29568, 144144, 686400, 3208920, 14780480, 67251184, 302865472, 1352078000, 5990745600, 26369978400, 115407434880, 502503206040, 2178032472000, 9401840170800, 40434981787200, 173319035569680, 740642835229440, 3156148445580000

Offset

0,1

References

R. C. Mullin, E. Nemeth and P. J. Schellenberg, The enumeration of almost cubic maps, pp. 281-295 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 1, edited R. C. Mullin et al., 1970.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

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

Links

Table of n, a(n) for n=0..22.

A. M. Mathai and P. N. Rathie, Enumeration of almost cubic maps, Journal of Combinatorial Theory, Series B, Vol 13 (1972), 83-90.

Formula

a(n) = 2*(n+3)*(2*(n+1))! / (3*n!*(n+1)!). [Mathai & Rathie, Eq. (22)] - Andrey Zabolotskiy, Jun 24 2024

Crossrefs

Cf. A002005, A002006, A002007, A002008, A002009, A002010, A002011.

Sequence in context: A043018 A270015 A271161 * A240408 A248216 A133642

Adjacent sequences: A002009 A002010 A002011 * A002013 A002014 A002015

Keyword

nonn

Author

N. J. A. Sloane

Extensions

Terms a(7) and beyond from Andrey Zabolotskiy, Jun 24 2024

Status

approved