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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 24 |
| 4 | 309 |
| 5 | 5262 |
| 6 | 108894 |
| 7 | 2618718 |
| 8 | 71246145 |
| 9 | 2154788970 |
| 10 | 71563126710 |
| 11 | 2586270267600 |
| 12 | 100995812044266 |
| 13 | 4237522832234832 |
| 14 | 190126298040192912 |
| 15 | 9085093650185205498 |
| 16 | 460711407231295513689 |
| 17 | 24715373661154672634058 |
| 18 | 1398648334415007990887454 |
[1,1,3,24,309,5262,108894,2618718,71246145, 2154788970,71563126710,2586270267600, 100995812044266,4237522832234832, 190126298040192912,9085093650185205498, 460711407231295513689,24715373661154672634058, 1398648334415007990887454] |