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%I #21 May 19 2024 14:03:09
%S 0,1,10,105,1176,13860,169884,2147145,27810640,367479684,4936848280,
%T 67255063876,927192688800,12914469594000,181497968832600,
%U 2570903476583625,36671501616314400,526348636137670500,7597019633665077000,110205019733436728100
%N Secondary root edges in doubly rooted tree maps with n edges.
%H Alois P. Heinz, <a href="/A046715/b046715.txt">Table of n, a(n) for n = 0..250</a>
%H R. C. Mullin, <a href="http://dx.doi.org/10.1016/S0021-9800(67)80001-2">On the average activity of a spanning tree of a rooted map</a>, J. Combin. Theory, 3 (1967), 103-121.
%H R. C. Mullin, <a href="/A260039/a260039.pdf">On the average activity of a spanning tree of a rooted map</a>, J. Combin. Theory, 3 (1967), 103-121. [Annotated scanned copy]
%F B(n) = (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!). - _Alois P. Heinz_, Dec 22 2011
%p B:= n-> (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!):
%p seq(B(n), n=0..20); # _Alois P. Heinz_, Dec 22 2011
%K nonn,easy
%O 0,3
%A _N. J. A. Sloane_
%E Corrected and extended by _Alois P. Heinz_, Dec 22 2011