A229048 Number of different chromatic polynomials of a simple graph with n nodes.
1, 2, 4, 9, 23, 73, 304, 1954, 23075, 607507
Offset: 1
Examples
From _Gus Wiseman_, Nov 24 2018: (Start) The a(4) = 9 chromatic polynomials: -6x + 11x^2 - 6x^3 + x^4 -4x + 8x^2 - 5x^3 + x^4 -2x + 5x^2 - 4x^3 + x^4 -3x + 6x^2 - 4x^3 + x^4 2x^2 - 3x^3 + x^4 -x + 3x^2 - 3x^3 + x^4 x^2 - 2x^3 + x^4 -x^3 + x^4 x^4 (End)
References
- F. M. Dong, K. M. Koh, and K. L. Teo. Chromatic Polynomials and Chromaticity of Graphs, World Scientific Publishing Company, 2005.
Links
- MathWorld, Chromatic Polynomial
- Eric M. Schmidt, The 304 polynomials for n=7
Crossrefs
Programs
-
Mathematica
spsu[,{}]:={{}};spsu[foo,set:{i_,_}]:=Join@@Function[s,Prepend[#,s]&/@spsu[Select[foo,Complement[#,Complement[set,s]]=={}&],Complement[set,s]]]/@Cases[foo,{i,_}]; falling[x_,k_]:=Product[(x-i),{i,0,k-1}]; chromPoly[g_]:=Expand[Sum[falling[x,Length[stn]],{stn,spsu[Select[Subsets[Union@@g],Select[DeleteCases[g,{_}],Function[ed,Complement[ed,#]=={}]]=={}&],Union@@g]}]]; simpleSpans[n_]:=simpleSpans[n]=If[n==0,{{}},Union@@Table[If[#=={},Union[ine,{{n}}],Union[Complement[ine,List/@#],{#,n}&/@#]]&/@Subsets[Range[n-1]],{ine,simpleSpans[n-1]}]]; Table[Length[Union[chromPoly/@simpleSpans[n]]],{n,5}] (* Gus Wiseman, Nov 24 2018 *)
-
Sage
def A229048(n): return len({g.chromatic_polynomial() for g in graphs(n)})
-
Sage
sorted({g.chromatic_polynomial() for g in graphs(n)})
Extensions
a(10) added by Eric M. Schmidt, Mar 20 2015
Comments