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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 24 |
| 6 | 840 |
| 7 | 720 |
| 8 | 5040 |
| 9 | 40320 |
| 10 | 59814720 |
| 11 | 3628800 |
| 12 | 83701537920 |
| 13 | 479001600 |
| 14 | 26980643289600 |
| 15 | 2642646473026560 |
| 16 | 1307674368000 |
| 17 | 20922789888000 |
| 18 | 41837259585747225600 |
| 19 | 6402373705728000 |
| 20 | 598354114828973074790400 |
| 21 | 18160977780223038067507200 |
[1,1,2,6,24,840,720,5040,40320,59814720,3628800, 83701537920,479001600,26980643289600, 2642646473026560,1307674368000,20922789888000, 41837259585747225600,6402373705728000, 598354114828973074790400, 18160977780223038067507200] |