A007748 Number of self-converse oriented trees with n nodes.

1, 1, 1, 2, 3, 7, 10, 26, 39, 107, 160, 458, 702, 2058, 3177, 9498, 14830, 44947, 70678, 216598, 342860, 1059952, 1686486, 5251806, 8393681, 26297238, 42187148, 132856766, 213828802, 676398395, 1091711076

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• nice

Links

• R. Simion, Trees with 1-factors and oriented trees, Discrete Math., 88 (1991), 93-104.
• R. Simion, Trees with 1-factors and oriented trees, Discrete Math., 88 (1981), 97. (Annotated scanned copy)
• Index entries for sequences related to trees

Crossrefs

Cf. A000238.

Programs

Mathematica

max = 15; A[n_, k_] := A[n, k] = If[n<2, n, Sum[Sum[d*A[d, k], {d, Divisors[j]}] * A[n-j, k]*k, {j, 1, n-1}]/(n-1)]; a[n_] := A[n, 2]; A000151 = Table[a[n], {n, 1, max}]; etr[p_] := Module[{b}, b[n_] := b[n] = If[n==0, 1, Sum[Sum[d*p[d], {d, Divisors[j]}]*b[n-j], {j, 1, n}]/n]; b]; A005750 = Table[etr[a][n], {n, 0, max}] ; A007748 = Riffle[A005750, A000151] (* Jean-François Alcover, Jul 16 2015 *)

Formula

a(2n)=A000151(n). a(2n-1)=A005750(n). - Christian G. Bower, Dec 15 1999