The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A324166 Number of totally crossing set partitions of {1,...,n}. 15
 1, 1, 1, 1, 2, 6, 18, 57, 207, 842, 3673, 17062, 84897 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS A set partition is totally crossing if every pair of distinct blocks is of the form {{...x...y...}, {...z...t...}} for some x < z < y < t or z < x < t < y. LINKS EXAMPLE The a(6) = 18 totally crossing set partitions:   {{1,2,3,4,5,6}}   {{1,4,6},{2,3,5}}   {{1,4,5},{2,3,6}}   {{1,3,6},{2,4,5}}   {{1,3,5},{2,4,6}}   {{1,3,4},{2,5,6}}   {{1,2,5},{3,4,6}}   {{1,2,4},{3,5,6}}   {{4,6},{1,2,3,5}}   {{3,6},{1,2,4,5}}   {{3,5},{1,2,4,6}}   {{2,6},{1,3,4,5}}   {{2,5},{1,3,4,6}}   {{2,4},{1,3,5,6}}   {{1,5},{2,3,4,6}}   {{1,4},{2,3,5,6}}   {{1,3},{2,4,5,6}}   {{1,4},{2,5},{3,6}} MATHEMATICA nn=6; nonXQ[stn_]:=!MatchQ[stn, {___, {___, x_, ___, y_, ___}, ___, {___, z_, ___, t_, ___}, ___}/; x

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

Last modified April 10 08:09 EDT 2021. Contains 342845 sequences. (Running on oeis4.)