A046647 Number of certain rooted planar maps.
1, 6, 26, 120, 594, 3094, 16728, 93024, 528770, 3058770, 17948970, 106585440, 639318456, 3867821640, 23574446992, 144621823632, 892293152994, 5533289372170, 34468829508750, 215594574231960, 1353464311979010
Offset: 2
Links
- W. G. Brown, Enumeration of non-separable planar maps, Canad. J. Math., 15 (1963), 526-545.
- W. G. Brown, Enumeration of non-separable planar maps [Annotated scanned copy]
Formula
a(2)=1; a(n) = 4*(7*n-15)*(3*n-6)!/((n-2)!*(2n-2)!). - Emeric Deutsch, Mar 03 2004
G.f.: (g+1)*(3*g+1)/(g-1)^2 where g*(1-g)^2 = x. - Mark van Hoeij, Nov 10 2011
Extensions
More terms from Emeric Deutsch, Mar 03 2004