cp's OEIS Frontend

A326362 Number of maximal intersecting antichains of nonempty, non-singleton subsets of {1..n}.

%I A326362 #15 May 26 2020 21:57:45
%S A326362 1,1,1,2,16,163,11742,12160640
%N A326362 Number of maximal intersecting antichains of nonempty, non-singleton subsets of {1..n}.
%C A326362 A set system (set of sets) is an antichain if no part is a subset of any other, and is intersecting if no two parts are disjoint.
%F A326362 For n > 1, a(n) = A326363(n) - n - 1 = A007363(n + 1) - n.
%e A326362 The a(4) = 16 maximal intersecting antichains:
%e A326362   {{1,2,3,4}}
%e A326362   {{1,2},{1,3},{2,3}}
%e A326362   {{1,2},{1,4},{2,4}}
%e A326362   {{1,3},{1,4},{3,4}}
%e A326362   {{2,3},{2,4},{3,4}}
%e A326362   {{1,2},{1,3,4},{2,3,4}}
%e A326362   {{1,3},{1,2,4},{2,3,4}}
%e A326362   {{1,4},{1,2,3},{2,3,4}}
%e A326362   {{2,3},{1,2,4},{1,3,4}}
%e A326362   {{2,4},{1,2,3},{1,3,4}}
%e A326362   {{3,4},{1,2,3},{1,2,4}}
%e A326362   {{1,2},{1,3},{1,4},{2,3,4}}
%e A326362   {{1,2},{2,3},{2,4},{1,3,4}}
%e A326362   {{1,3},{2,3},{3,4},{1,2,4}}
%e A326362   {{1,4},{2,4},{3,4},{1,2,3}}
%e A326362   {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}
%t A326362 stableSets[u_,Q_]:=If[Length[u]==0,{{}},With[{w=First[u]},Join[stableSets[DeleteCases[u,w],Q],Prepend[#,w]&/@stableSets[DeleteCases[u,r_/;r==w||Q[r,w]||Q[w,r]],Q]]]];
%t A326362 fasmax[y_]:=Complement[y,Union@@(Most[Subsets[#]]&/@y)];
%t A326362 Table[Length[fasmax[stableSets[Subsets[Range[n],{2,n}],Or[Intersection[#1,#2]=={},SubsetQ[#1,#2]]&]]],{n,0,5}]
%t A326362 (* 2nd program *)
%t A326362 n = 2^6; g = CompleteGraph[n]; i = 0;
%t A326362 While[i < n, i++; j = i; While[j < n, j++; If[BitAnd[i, j] == 0 || BitAnd[i, j] == i || BitAnd[i, j] == j, g = EdgeDelete[g, i <-> j]]]];
%t A326362 sets = FindClique[g, Infinity, All];
%t A326362 Length[sets]-Log[2,n]-1 (* _Elijah Beregovsky_, May 06 2020 *)
%Y A326362 Antichains of nonempty, non-singleton sets are A307249.
%Y A326362 Minimal covering antichains are A046165.
%Y A326362 Maximal intersecting antichains are A007363.
%Y A326362 Maximal antichains of nonempty sets are A326359.
%Y A326362 Cf. A000372, A003182, A006126, A006602, A014466, A051185, A058891, A261005, A305000, A305844, A326358, A326360, A326361, A326363.
%K A326362 nonn,more
%O A326362 0,4
%A A326362 _Gus Wiseman_, Jul 01 2019
%E A326362 a(7) from _Elijah Beregovsky_, May 06 2020