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A321911 Number of distinct chromatic symmetric functions of simple connected graphs with n vertices. 11
1, 1, 2, 6, 20, 103, 759 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A stable partition of a graph is a set partition of the vertices where no edge has both ends in the same block. The chromatic symmetric function is given by X_G = Sum_p m(t(p)) where the sum is over all stable partitions p of G, t(p) is the integer partition whose parts are the block-sizes of p, and m is augmented monomial symmetric functions (see A321895).

LINKS

Table of n, a(n) for n=1..7.

Richard P. Stanley, A symmetric function generalization of the chromatic polynomial of a graph, Advances in Math. 111 (1995), 166-194.

Richard P. Stanley, Graph colorings and related symmetric functions: ideas and applications, Discrete Mathematics 193 (1998), 267-286.

Gus Wiseman, A partition of connected graphs, Electronic J. Combinatorics 12, N1 (2005), 8pp. arXiv:math/0505155 [math.CO].

EXAMPLE

The a(4) = 6 connected chromatic symmetric functions (m is the augmented monomial symmetric function basis):

                    m(1111)

           m(211) + m(1111)

          2m(211) + m(1111)

  m(22) + 2m(211) + m(1111)

  m(22) + 3m(211) + m(1111)

  m(31) + 3m(211) + m(1111)

MATHEMATICA

spsu[_, {}]:={{}}; spsu[foo_, set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@spsu[Select[foo, Complement[#, Complement[set, s]]=={}&], Complement[set, s]]]/@Cases[foo, {i, ___}];

chromSF[g_]:=Sum[m[Sort[Length/@stn, Greater]], {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]}]];

csm[s_]:=With[{c=Select[Tuples[Range[Length[s]], 2], And[OrderedQ[#], UnsameQ@@#, Length[Intersection@@s[[#]]]>0]&]}, If[c=={}, s, csm[Union[Append[Delete[s, List/@c[[1]]], Union@@s[[c[[1]]]]]]]]];

Table[Length[Union[chromSF/@Select[simpleSpans[n], Length[csm[#]]==1&]]], {n, 6}]

CROSSREFS

First differs from A079457 at a(7) = 759, A079457(7) = 706.

Cf. A000110, A001349, A001187, A125702, A147878, A191970, A229048, A240936, A245883, A277203, A317631, A317632, A320921, A321750, A321751, A321895.

Sequence in context: A003094 A073964 A079457 * A079455 A052433 A078566

Adjacent sequences:  A321908 A321909 A321910 * A321912 A321913 A321914

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Nov 21 2018

STATUS

approved

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Last modified March 28 07:59 EDT 2020. Contains 333079 sequences. (Running on oeis4.)