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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 218 |
| 5 | 2331 |
| 6 | 29152 |
| 7 | 417607 |
| 8 | 6746700 |
| 9 | 121312441 |
| 10 | 2401341056 |
| 11 | 51857779689 |
| 12 | 1212621122176 |
| 13 | 30509979042115 |
| 14 | 821524617293304 |
| 15 | 23563369209520711 |
| 16 | 717014609781379568 |
| 17 | 23064363484845390513 |
[1,1,4,25,218,2331,29152,417607,6746700,121312441, 2401341056,51857779689,1212621122176, 30509979042115,821524617293304,23563369209520711, 717014609781379568,23064363484845390513] |