vdist[v_,w_]:=总数[Abs[v-w]];
flowdown[prs_]:=并集[prs,With[{ovs=Select[Subsets[prs、{2}],vdist@@#==2&]},并集@@Function[{v,w},Select[Tuples[{Range[Min@@Union[First/@prs],Max@@Union[First/@prs]],Range[Min@@Union[Clast/@prs],Max@Union[Last/@prs]]}],vdist[v,#]=1&&vdist[w,#]=1&]]@@@ovs]];
表[Length[Select[Subsets[Tuples[Range[n],2]],flowdown[#]==#&]],{n,0,3}]
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