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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A327335 Number of non-isomorphic set-systems with n vertices and at least one endpoint/leaf. 5
 0, 1, 4, 18, 216 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS A set-system is a finite set of finite nonempty sets. Elements of a set-system are sometimes called edges. A leaf is an edge containing a vertex that does not belong to any other edge, while an endpoint is a vertex belonging to only one edge. Also covering set-systems with minimum covered vertex-degree 1. LINKS Table of n, a(n) for n=0..4. EXAMPLE Non-isomorphic representatives of the a(1) = 1 through a(3) = 18 set-systems: {{1}} {{1}} {{1}} {{1,2}} {{1,2}} {{1},{2}} {{1},{2}} {{1},{1,2}} {{1,2,3}} {{1},{1,2}} {{1},{2,3}} {{1},{1,2,3}} {{1,2},{1,3}} {{1},{2},{3}} {{1,2},{1,2,3}} {{1},{2},{1,3}} {{1},{1,2},{1,3}} {{1},{1,2},{2,3}} {{1},{2},{1,2,3}} {{1},{1,2},{1,2,3}} {{1},{2},{3},{1,2}} {{1},{2},{1,2},{1,3}} {{1},{2},{1,2},{1,2,3}} CROSSREFS Unlabeled set-systems are A000612. The labeled version is A327228. The covering version is A327230 (first differences). Cf. A002494, A245797, A261919, A283877, A327103, A327105, A327197, A327227, A327229, A327336. Sequence in context: A356561 A197786 A242083 * A275965 A363313 A071173 Adjacent sequences: A327332 A327333 A327334 * A327336 A327337 A327338 KEYWORD nonn,more AUTHOR Gus Wiseman, Sep 02 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 September 29 02:45 EDT 2023. Contains 365749 sequences. (Running on oeis4.)