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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 91 |
| 4 | 613 |
| 5 | 4408 |
| 6 | 33143 |
| 7 | 257400 |
| 8 | 2048825 |
| 9 | 16625940 |
| 10 | 137033316 |
| 11 | 1144010387 |
| 12 | 9653706723 |
| 13 | 82208879366 |
| 14 | 705587243802 |
| 15 | 6097408839400 |
| 16 | 53007770199641 |
| 17 | 463269048213536 |
| 18 | 4067950092964440 |
| 19 | 35871913838983980 |
| 20 | 317533385082542404 |
| 21 | 2820492099258807887 |
[1,3,15,91,613,4408,33143,257400,2048825,16625940, 137033316,1144010387,9653706723,82208879366, 705587243802,6097408839400,53007770199641, 463269048213536,4067950092964440, 35871913838983980,317533385082542404, 2820492099258807887] |