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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 18 |
| 4 | 360 |
| 5 | 7560 |
| 6 | 289440 |
| 7 | 9828000 |
| 8 | 631169280 |
| 9 | 46449002880 |
| 10 | 4526271187200 |
| 11 | 524461965350400 |
| 12 | 74044329341875200 |
| 13 | 12211524764030592000 |
[0,1,18,360,7560,289440,9828000,631169280, 46449002880,4526271187200,524461965350400, 74044329341875200,12211524764030592000] |