Number of ways to partition n labeled elements into 4 pie slices allowing the pie to be turned over; number of 2-element proper antichains of an n-element set.
A032263
Number of ways to partition n labeled elements into 4 pie slices allowing the pie to be turned over; number of 2-element proper antichains of an n-element set.
Terms
- a(0) =0a(1) =0a(2) =0a(3) =3a(4) =30a(5) =195a(6) =1050a(7) =5103a(8) =23310a(9) =102315a(10) =437250a(11) =1834503a(12) =7597590a(13) =31175235a(14) =127067850a(15) =515396703a(16) =2083011870a(17) =8396420955a(18) =33779000850a(19) =135696347703a(20) =544527210150
External references
- oeis: A032263