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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 30 |
| 4 | 143 |
| 5 | 660 |
| 6 | 3000 |
| 7 | 13448 |
| 8 | 59696 |
| 9 | 262788 |
| 10 | 1148738 |
| 11 | 4989908 |
| 12 | 21551733 |
| 13 | 92596511 |
| 14 | 395921737 |
| 15 | 1685304092 |
| 16 | 7143861196 |
| 17 | 30163965903 |
| 18 | 126895681419 |
| 19 | 531986033218 |
| 20 | 2222961809367 |
| 21 | 9260148591001 |
| 22 | 38461580964389 |
| 23 | 159302487751844 |
| 24 | 658054630483936 |
| 25 | 2711429650817356 |
[1,1,6,30,143,660,3000,13448,59696,262788,1148738, 4989908,21551733,92596511,395921737,1685304092, 7143861196,30163965903,126895681419,531986033218, 2222961809367,9260148591001,38461580964389, 159302487751844,658054630483936,2711429650817356] |