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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 8 |
| 5 | 40 |
| 6 | 168 |
| 7 | 504 |
| 8 | 3456 |
| 9 | 15552 |
| 10 | 97920 |
| 11 | 620928 |
| 12 | 4465152 |
| 13 | 31449600 |
| 14 | 273369600 |
| 15 | 2172096000 |
| 16 | 20968243200 |
| 17 | 192753561600 |
| 18 | 2032260710400 |
| 19 | 20942298316800 |
| 20 | 243270107136000 |
| 21 | 2758764950323200 |
| 22 | 34958441123020800 |
| 23 | 434690126954496000 |
| 24 | 5946571752210432000 |
| 25 | 80503989505228800000 |
[1,2,6,8,40,168,504,3456,15552,97920,620928, 4465152,31449600,273369600,2172096000,20968243200, 192753561600,2032260710400,20942298316800, 243270107136000,2758764950323200, 34958441123020800,434690126954496000, 5946571752210432000,80503989505228800000] |