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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 40 |
| 3 | 264 |
| 4 | 1620 |
| 5 | 9156 |
| 6 | 49848 |
| 7 | 264300 |
| 8 | 1374048 |
| 9 | 7036116 |
| 10 | 35600376 |
| 11 | 178380156 |
| 12 | 886616784 |
| 13 | 4377006372 |
| 14 | 21483378600 |
| 15 | 104919416268 |
| 16 | 510169843584 |
| 17 | 2471194910580 |
| 18 | 11929478452824 |
| 19 | 57413851328028 |
| 20 | 275566856985648 |
[0,40,264,1620,9156,49848,264300,1374048,7036116, 35600376,178380156,886616784,4377006372, 21483378600,104919416268,510169843584, 2471194910580,11929478452824,57413851328028, 275566856985648] |