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| n | a(n) |
|---|---|
| 2 | 2 |
| 3 | 10 |
| 4 | 60 |
| 5 | 396 |
| 6 | 2976 |
| 7 | 25056 |
| 8 | 234720 |
| 9 | 2423520 |
| 10 | 27371520 |
| 11 | 335819520 |
| 12 | 4449150720 |
| 13 | 63318931200 |
| 14 | 963548006400 |
| 15 | 15614378035200 |
| 16 | 268480048435200 |
| 17 | 4882321001779200 |
| 18 | 93627018326016000 |
| 19 | 1888394741194752000 |
| 20 | 39963486306078720000 |
| 21 | 885457095215616000000 |
[2,10,60,396,2976,25056,234720,2423520,27371520, 335819520,4449150720,63318931200,963548006400, 15614378035200,268480048435200,4882321001779200, 93627018326016000,1888394741194752000, 39963486306078720000,885457095215616000000] |