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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 33 |
| 4 | 615 |
| 5 | 6997 |
| 6 | 53950 |
| 7 | 315198 |
| 8 | 1499394 |
| 9 | 6083808 |
| 10 | 21733215 |
| 11 | 69921908 |
| 12 | 206052448 |
| 13 | 563440284 |
| 14 | 1444285973 |
| 15 | 3499040581 |
| 16 | 8065603025 |
| 17 | 17787652381 |
| 18 | 37705694442 |
| 19 | 77126966988 |
| 20 | 152747362302 |
| 21 | 293741640632 |
| 22 | 549886035657 |
[0,1,33,615,6997,53950,315198,1499394,6083808, 21733215,69921908,206052448,563440284,1444285973, 3499040581,8065603025,17787652381,37705694442, 77126966988,152747362302,293741640632, 549886035657] |