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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 52 |
| 6 | 199 |
| 7 | 722 |
| 8 | 2693 |
| 9 | 10052 |
| 10 | 37344 |
| 11 | 141943 |
| 12 | 528323 |
| 13 | 2020746 |
| 14 | 7720299 |
| 15 | 29535575 |
| 16 | 112041465 |
| 17 | 434810382 |
| 18 | 1666519344 |
| 19 | 6447232492 |
| 20 | 24895996003 |
| 21 | 96654652273 |
[0,1,3,15,52,199,722,2693,10052,37344,141943, 528323,2020746,7720299,29535575,112041465, 434810382,1666519344,6447232492,24895996003, 96654652273] |