| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 201 |
| 5 | 2604 |
| 6 | 40915 |
| 7 | 754368 |
| 8 | 15960945 |
| 9 | 381141008 |
| 10 | 10139372451 |
| 11 | 297356237760 |
| 12 | 9530800099513 |
| 13 | 331453265976000 |
| 14 | 12430323314648499 |
| 15 | 500046099516905984 |
| 16 | 21478615942550889825 |
| 17 | 981110493372418629888 |
| 18 | 47489191763845877910595 |
[1,1,3,20,201,2604,40915,754368,15960945, 381141008,10139372451,297356237760,9530800099513, 331453265976000,12430323314648499, 500046099516905984,21478615942550889825, 981110493372418629888,47489191763845877910595] |