The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A326964 Number of connected set-systems covering a subset of {1..n}. 1
 1, 2, 7, 112, 32253, 2147316942, 9223372023968335715, 170141183460469231667123699322514272668, 5789604461865809771178549250434395393752402807429031284280914691514037561273 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A set-system is a finite set of finite nonempty sets. LINKS Table of n, a(n) for n=0..8. FORMULA Binomial transform of A323818. EXAMPLE The a(0) = 1 through a(2) = 7 set-systems: {} {} {} {{1}} {{1}} {{2}} {{1,2}} {{1},{1,2}} {{2},{1,2}} {{1},{2},{1,2}} MATHEMATICA csm[s_]:=With[{c=Select[Tuples[Range[Length[s]], 2], And[OrderedQ[#], UnsameQ@@#, Length[Intersection@@s[[#]]]>0]&]}, If[c=={}, s, csm[Sort[Append[Delete[s, List/@c[[1]]], Union@@s[[c[[1]]]]]]]]]; Table[Length[Select[Subsets[Subsets[Range[n], {1, n}]], Length[csm[#]]<=1&]], {n, 0, 4}] CROSSREFS Covering sets of subsets are A000371. Connected graphs are A001187. The unlabeled version is A309667. The BII-numbers of connected set-systems are A326749. The covering case is A323818. Cf. A007718, A048143, A058891, A092918, A300913, A304716, A326866, A326948. Sequence in context: A000157 A264999 A326940 * A034902 A101429 A270749 Adjacent sequences: A326961 A326962 A326963 * A326965 A326966 A326967 KEYWORD nonn AUTHOR Gus Wiseman, Aug 10 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 3 18:52 EST 2023. Contains 367540 sequences. (Running on oeis4.)