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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 25 |
| 6 | 90 |
| 7 | 350 |
| 8 | 1701 |
| 9 | 6951 |
| 10 | 42525 |
| 11 | 179487 |
| 12 | 1323652 |
| 13 | 5715424 |
| 14 | 49329280 |
| 15 | 216627840 |
| 16 | 2141764053 |
| 17 | 9528822303 |
| 18 | 106175395755 |
| 19 | 477297033785 |
| 20 | 5917584964655 |
| 21 | 26826851689001 |
| 22 | 366282500870286 |
| 23 | 1672162773483930 |
| 24 | 24930204590758260 |
| 25 | 114485073343744260 |
[1,1,1,3,7,25,90,350,1701,6951,42525,179487, 1323652,5715424,49329280,216627840,2141764053, 9528822303,106175395755,477297033785, 5917584964655,26826851689001,366282500870286, 1672162773483930,24930204590758260, 114485073343744260] |