OFFSET
1,2
EXAMPLE
The T(3,2) = 6 pairs of set partitions:
{{1},{2},{3}} {{1},{2,3}}
{{1},{2},{3}} {{1,2},{3}}
{{1},{2},{3}} {{1,3},{2}}
{{1},{2,3}} {{1},{2},{3}}
{{1,2},{3}} {{1},{2},{3}}
{{1,3},{2}} {{1},{2},{3}}
Triangle begins:
1
2 1
8 6 1
56 44 12 1
552 440 140 20 1
7202 5632 1920 340 30 1
MATHEMATICA
sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}];
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]]]]]]]]];
spmeet[a_, b_]:=DeleteCases[Union@@Outer[Intersection, a, b, 1], {}]; spmeet[a_, b_, c__]:=spmeet[spmeet[a, b], c];
Table[Length[Select[Tuples[sps[Range[n]], 2], And[Max@@Length/@spmeet@@#==1, Length[csm[Union@@#]]==k]&]], {n, 5}, {k, n}]
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Gus Wiseman, Aug 25 2018
STATUS
approved