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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 84 |
| 4 | 495 |
| 5 | 3003 |
| 6 | 18564 |
| 7 | 116280 |
| 8 | 735471 |
| 9 | 4686825 |
| 10 | 30045015 |
| 11 | 193536720 |
| 12 | 1251677700 |
| 13 | 8122425444 |
| 14 | 52860229080 |
| 15 | 344867425584 |
| 16 | 2254848913647 |
| 17 | 14771069086725 |
| 18 | 96926348578605 |
| 19 | 636983969321700 |
| 20 | 4191844505805495 |
| 21 | 27619435402363035 |
[1,3,15,84,495,3003,18564,116280,735471,4686825, 30045015,193536720,1251677700,8122425444, 52860229080,344867425584,2254848913647, 14771069086725,96926348578605,636983969321700, 4191844505805495,27619435402363035] |