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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 12 |
| 5 | 120 |
| 6 | 1200 |
| 7 | 12600 |
| 8 | 141120 |
| 9 | 1693440 |
| 10 | 21772800 |
| 11 | 299376000 |
| 12 | 4390848000 |
| 13 | 68497228800 |
| 14 | 1133317785600 |
| 15 | 19833061248000 |
| 16 | 366148823040000 |
| 17 | 7113748561920000 |
| 18 | 145120470663168000 |
| 19 | 3101950060425216000 |
| 20 | 69337707233034240000 |
| 21 | 1617879835437465600000 |
[0,0,1,12,120,1200,12600,141120,1693440,21772800, 299376000,4390848000,68497228800,1133317785600, 19833061248000,366148823040000,7113748561920000, 145120470663168000,3101950060425216000, 69337707233034240000,1617879835437465600000] |