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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 480 |
| 6 | 3960 |
| 7 | 40320 |
| 8 | 463680 |
| 9 | 5866560 |
| 10 | 82857600 |
| 11 | 1297296000 |
| 12 | 22133865600 |
| 13 | 407869862400 |
| 14 | 8096683795200 |
| 15 | 172405968134400 |
| 16 | 3915525770956800 |
| 17 | 94443904345190400 |
| 18 | 2412049832704512000 |
| 19 | 65035187612185190400 |
| 20 | 1845812342328514560000 |
[1,1,2,12,72,480,3960,40320,463680,5866560, 82857600,1297296000,22133865600,407869862400, 8096683795200,172405968134400,3915525770956800, 94443904345190400,2412049832704512000, 65035187612185190400,1845812342328514560000] |