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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4320 |
| 3 | 61440 |
| 4 | 522720 |
| 5 | 2211840 |
| 6 | 8960640 |
| 7 | 23224320 |
| 8 | 67154400 |
| 9 | 135168000 |
| 10 | 319809600 |
| 11 | 550195200 |
| 12 | 1147643520 |
| 13 | 1771683840 |
| 14 | 3371915520 |
| 15 | 4826603520 |
| 16 | 8593797600 |
| 17 | 11585617920 |
| 18 | 19590534240 |
| 19 | 25239859200 |
| 20 | 40979580480 |
| 21 | 50877235200 |
[1,0,4320,61440,522720,2211840,8960640,23224320, 67154400,135168000,319809600,550195200,1147643520, 1771683840,3371915520,4826603520,8593797600, 11585617920,19590534240,25239859200,40979580480, 50877235200] |