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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 66 |
| 7 | 221 |
| 8 | 757 |
| 9 | 2647 |
| 10 | 9402 |
| 11 | 33813 |
| 12 | 122876 |
| 13 | 450543 |
| 14 | 1664835 |
| 15 | 6193553 |
| 16 | 23178525 |
| 17 | 87199503 |
| 18 | 329592705 |
| 19 | 1251029482 |
| 20 | 4766563155 |
| 21 | 18223733493 |
| 22 | 69892469057 |
| 23 | 268824143700 |
| 24 | 1036690445777 |
| 25 | 4007586822784 |
[1,1,2,6,20,66,221,757,2647,9402,33813,122876, 450543,1664835,6193553,23178525,87199503, 329592705,1251029482,4766563155,18223733493, 69892469057,268824143700,1036690445777, 4007586822784] |