A217861 Number of functions on n unlabeled nodes in which all the components are distinct.

1, 1, 2, 6, 14, 38, 103, 280, 773, 2160, 6053, 17064, 48320, 137260, 391091, 1117192, 3198217, 9173480, 26357393, 75845591, 218550709, 630536447, 1821184411, 5265514692, 15238183779, 44136519841, 127940010907, 371135327740, 1077340058523, 3129301019091, 7015876423459

Offset: 0

Author

Geoffrey Critzer, Oct 13 2012

Keywords

• nonn

Programs

Mathematica

Needs["Combinatorica`"];
nn=30;s[n_,k_]:=s[n,k]=a[n+1-k]+If[n<2 k,0,s[n-k,k]];a[1]=1;a[n_]:=a[n]=Sum[a[i] s[n-1,i] i,{i,1,n-1}]/(n-1);rt=Table[a[i],{i,1,nn}];c=Drop[Apply[Plus,Table[Take[CoefficientList[CycleIndex[CyclicGroup[n],s]/.Table[s[j]->Table[Sum[rt[[i]] x^(k*i),{i,1,nn}],{k,1,nn}][[j]],{j,1,nn}],x],nn],{n,1,30}]],1];CoefficientList[Series[Product[(1+ x^i)^c[[i]],{i,1,nn-1}],{x,0,nn}],x]  (* after code given by Robert A. Russell in A000081 *)

Formula

O.g.f.: Product_{n>=1} (1 + x^n)^A002861(n).