A046715 Secondary root edges in doubly rooted tree maps with n edges.

0, 1, 10, 105, 1176, 13860, 169884, 2147145, 27810640, 367479684, 4936848280, 67255063876, 927192688800, 12914469594000, 181497968832600, 2570903476583625, 36671501616314400, 526348636137670500, 7597019633665077000, 110205019733436728100

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..250
• R. C. Mullin, On the average activity of a spanning tree of a rooted map, J. Combin. Theory, 3 (1967), 103-121.
• R. C. Mullin, On the average activity of a spanning tree of a rooted map, J. Combin. Theory, 3 (1967), 103-121. [Annotated scanned copy]

Programs

Maple

B:= n-> (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!):
seq(B(n), n=0..20); # Alois P. Heinz, Dec 22 2011

Formula

B(n) = (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!). - Alois P. Heinz, Dec 22 2011

Extensions

Corrected and extended by Alois P. Heinz, Dec 22 2011