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A007748 Number of self-converse oriented trees with n nodes. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..31.

R. Simion, Trees with 1-factors and oriented trees, Discrete Math., 88 (1991), 93-104.

R. Simon, Trees with 1-factors and oriented trees, Discrete Math., 88 (1981), 97. (Annotated scanned copy)

Index entries for sequences related to trees

FORMULA

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

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-Fran├žois Alcover, Jul 16 2015 *)

CROSSREFS

Cf. A000238.

Sequence in context: A263402 A062113 A130968 * A126617 A117733 A066236

Adjacent sequences:  A007745 A007746 A007747 * A007749 A007750 A007751

KEYWORD

nonn,nice

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified November 18 07:19 EST 2019. Contains 329250 sequences. (Running on oeis4.)