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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2820 |
| 7 | 31500 |
| 8 | 393568 |
| 9 | 5111568 |
| 10 | 78491520 |
| 11 | 1345893120 |
| 12 | 24286008384 |
| 13 | 483716087712 |
| 14 | 10526811186528 |
| 15 | 241867328844960 |
| 16 | 5957816820215040 |
| 17 | 157412355684364800 |
| 18 | 4380674530640290560 |
| 19 | 128826276098289179904 |
| 20 | 4010282529115722232320 |
[1,1,2,6,48,360,2820,31500,393568,5111568, 78491520,1345893120,24286008384,483716087712, 10526811186528,241867328844960,5957816820215040, 157412355684364800,4380674530640290560, 128826276098289179904,4010282529115722232320] |