Number of set partitions of {1, ..., n} that avoid 4-crossings.

A108305

Number of set partitions of {1, ..., n} that avoid 4-crossings.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =52a(6) =203a(7) =877a(8) =4139a(9) =21119a(10) =115495a(11) =671969a(12) =4132936a(13) =26723063a(14) =180775027a(15) =1274056792a(16) =9320514343a(17) =70548979894a(18) =550945607475

External references