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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 23 |
| 4 | 108 |
| 5 | 601 |
| 6 | 3874 |
| 7 | 28448 |
| 8 | 234903 |
| 9 | 2158498 |
| 10 | 21883451 |
| 11 | 243025718 |
| 12 | 2938265815 |
| 13 | 38469994687 |
| 14 | 542905969228 |
| 15 | 8224586470983 |
| 16 | 133260591917731 |
| 17 | 2301776455966976 |
| 18 | 42258406133001866 |
| 19 | 822404997883448574 |
[1,2,6,23,108,601,3874,28448,234903,2158498, 21883451,243025718,2938265815,38469994687, 542905969228,8224586470983,133260591917731, 2301776455966976,42258406133001866, 822404997883448574] |