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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 56 |
| 4 | 294 |
| 5 | 1698 |
| 6 | 10624 |
| 7 | 71256 |
| 8 | 508188 |
| 9 | 3829652 |
| 10 | 30340464 |
| 11 | 251647872 |
| 12 | 2177440648 |
| 13 | 19596586584 |
| 14 | 182967013056 |
| 15 | 1768251873632 |
| 16 | 17653554391056 |
| 17 | 181748836240944 |
| 18 | 1926542292294592 |
| 19 | 20996051677557888 |
| 20 | 234959167687868256 |
| 21 | 2696726674789023008 |
[1,3,12,56,294,1698,10624,71256,508188,3829652, 30340464,251647872,2177440648,19596586584, 182967013056,1768251873632,17653554391056, 181748836240944,1926542292294592, 20996051677557888,234959167687868256, 2696726674789023008] |