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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 24 |
| 5 | 144 |
| 6 | 480 |
| 7 | 4320 |
| 8 | 40320 |
| 9 | 282240 |
| 10 | 4354560 |
| 11 | 36288000 |
| 12 | 319334400 |
| 13 | 6706022400 |
| 14 | 74724249600 |
| 15 | 1046139494400 |
| 16 | 20922789888000 |
| 17 | 376610217984000 |
| 18 | 4979623993344000 |
| 19 | 115242726703104000 |
| 20 | 2919482409811968000 |
| 21 | 29194824098119680000 |
[1,2,4,24,144,480,4320,40320,282240,4354560, 36288000,319334400,6706022400,74724249600, 1046139494400,20922789888000,376610217984000, 4979623993344000,115242726703104000, 2919482409811968000,29194824098119680000] |