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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 520 |
| 6 | 5640 |
| 7 | 73500 |
| 8 | 1118880 |
| 9 | 19501776 |
| 10 | 383110560 |
| 11 | 8377205760 |
| 12 | 201831315840 |
| 13 | 5312936154240 |
| 14 | 151725201788160 |
| 15 | 4672298462832000 |
| 16 | 154342559776204800 |
| 17 | 5444359223483980800 |
| 18 | 204256674378018662400 |
| 19 | 8121472917226507238400 |
| 20 | 341153109889323443712000 |
[1,1,2,9,60,520,5640,73500,1118880,19501776, 383110560,8377205760,201831315840,5312936154240, 151725201788160,4672298462832000, 154342559776204800,5444359223483980800, 204256674378018662400,8121472917226507238400, 341153109889323443712000] |