The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 11 |
| 5 | 62 |
| 6 | 342 |
| 7 | 2152 |
| 8 | 13768 |
| 9 | 91800 |
| 10 | 622616 |
| 11 | 4301792 |
| 12 | 30100448 |
| 13 | 213019072 |
| 14 | 1521473984 |
| 15 | 10954616064 |
| 16 | 79420280064 |
| 17 | 579300888960 |
| 18 | 4248201302400 |
| 19 | 31302536066560 |
| 20 | 231638727063040 |
[1,1,3,11,62,342,2152,13768,91800,622616,4301792, 30100448,213019072,1521473984,10954616064, 79420280064,579300888960,4248201302400, 31302536066560,231638727063040] |