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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 4 |
| 4 | 20 |
| 5 | 114 |
| 6 | 750 |
| 7 | 5616 |
| 8 | 47304 |
| 9 | 443400 |
| 10 | 4582200 |
| 11 | 51790320 |
| 12 | 635791680 |
| 13 | 8426915280 |
| 14 | 119960552880 |
| 15 | 1825701857280 |
| 16 | 29585590473600 |
| 17 | 508653914267520 |
| 18 | 9248148480574080 |
| 19 | 177303557272262400 |
| 20 | 3574966680853747200 |
| 21 | 75628468328518828800 |
| 22 | 1675003757666567328000 |
[1,4,20,114,750,5616,47304,443400,4582200, 51790320,635791680,8426915280,119960552880, 1825701857280,29585590473600,508653914267520, 9248148480574080,177303557272262400, 3574966680853747200,75628468328518828800, 1675003757666567328000] |