A001433 Number of graphs with n nodes and n-1 edges. (Formerly M2588 N1024)

1, 1, 1, 3, 6, 15, 41, 115, 345, 1103, 3664, 12763, 46415, 175652, 691001, 2821116, 11932174, 52211412, 236007973, 1100528508, 5287050500, 26134330813, 132760735671, 692294900849, 3701754158688, 20275893222445, 113657560920970, 651449039159673, 3814790900995022, 22805438484189851

Offset

1,4

References

J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 146.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Sean A. Irvine, Table of n, a(n) for n = 1..40

M. L. Stein and P. R. Stein, Enumeration of Linear Graphs and Connected Linear Graphs up to p = 18 Points. Report LA-3775, Los Alamos Scientific Laboratory of the University of California, Los Alamos, NM, Oct 1967

Mathematica

Needs["Combinatorica`"]
Table[ NumberOfGraphs[n, n-1], {n, 1, 25}] (* Robert G. Wilson v *)
(* Second program (not needing Combinatorica): *)
permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];
edges[v_, t_] := Product[Product[g = GCD[v[[i]], v[[j]]]; t[v[[i]]* v[[j]]/g]^g, {j, 1, i - 1}], {i, 2, Length[v]}]*Product[c = v[[i]]; t[c]^Quotient[c - 1, 2]*If[OddQ[c], 1, t[c/2]], {i, 1, Length[v]}];
a[n_] := a[n] = Module[{s = 0}, Do[s += permcount[p]*edges[p, 1 + x^# &], {p, IntegerPartitions[n]}]; s/n!] // Expand // SeriesCoefficient[#, {x, 0, n-1}]&;
Table[Print[n, " ", a[n]]; a[n], {n, 1, 35}] (* Jean-François Alcover, Aug 18 2022, after Andrew Howroyd in A008406 *)

Crossrefs

Cf. A008406.

Sequence in context: A218777 A152799 A140824 * A005368 A067771 A289678

Adjacent sequences: A001430 A001431 A001432 * A001434 A001435 A001436

Keyword

nonn,easy,nice

Author

N. J. A. Sloane

Extensions

More terms from Vladeta Jovovic, Jan 15 2000

Status

approved