Number of set partitions of {1, ..., n} whose blocks are all singletons and pairs, not including {1, n} or {i, i + 1} for any i.
A306419
Number of set partitions of {1, ..., n} whose blocks are all singletons and pairs, not including {1, n} or {i, i + 1} for any i.
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =4a(5) =11a(6) =32a(7) =99a(8) =326a(9) =1123a(10) =4064a(11) =15291a(12) =59924a(13) =242945a(14) =1019584a(15) =4409233a(16) =19648674a(17) =89938705a(18) =422744384a(19) =2035739041a(20) =10039057524a(21) =50610247483a(22) =260704414816
External references
- oeis: A306419