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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 5040 |
| 8 | 40320 |
| 9 | 362880 |
| 10 | 3548160 |
| 11 | 37054080 |
| 12 | 416551680 |
| 13 | 5050368000 |
| 14 | 65944535040 |
| 15 | 924630958080 |
| 16 | 13873661706240 |
| 17 | 221978587299840 |
| 18 | 3774394191052800 |
| 19 | 67494538767237120 |
| 20 | 1276009602375352320 |
| 21 | 25429720417085030400 |
[1,1,2,6,24,120,720,5040,40320,362880,3548160, 37054080,416551680,5050368000,65944535040, 924630958080,13873661706240,221978587299840, 3774394191052800,67494538767237120, 1276009602375352320,25429720417085030400] |