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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 266 |
| 5 | 3599 |
| 6 | 62941 |
| 7 | 1372117 |
| 8 | 36248765 |
| 9 | 1135864306 |
| 10 | 41501271477 |
| 11 | 1743624004536 |
| 12 | 83268125043937 |
| 13 | 4476101995389591 |
| 14 | 268589319338401864 |
| 15 | 17860954789864760357 |
| 16 | 1307982591075162739660 |
| 17 | 104895999816356419875935 |
| 18 | 9166919404389461922512723 |
[1,1,4,27,266,3599,62941,1372117,36248765, 1135864306,41501271477,1743624004536, 83268125043937,4476101995389591, 268589319338401864,17860954789864760357, 1307982591075162739660,104895999816356419875935, 9166919404389461922512723] |