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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 3 |
| 5 | 8 |
| 6 | 24 |
| 7 | 84 |
| 8 | 420 |
| 9 | 2268 |
| 10 | 13440 |
| 11 | 73920 |
| 12 | 604800 |
| 13 | 3931200 |
| 14 | 33633600 |
| 15 | 324324000 |
| 16 | 3891888000 |
| 17 | 33081048000 |
| 18 | 435891456000 |
| 19 | 4140968832000 |
| 20 | 59281238016000 |
| 21 | 840311548876800 |
| 22 | 11708340914350080 |
| 23 | 134645920515025920 |
| 24 | 2554547108585472000 |
| 25 | 45616912653312000000 |
[1,1,2,3,8,24,84,420,2268,13440,73920,604800, 3931200,33633600,324324000,3891888000,33081048000, 435891456000,4140968832000,59281238016000, 840311548876800,11708340914350080, 134645920515025920,2554547108585472000, 45616912653312000000] |