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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 192 |
| 4 | 1728 |
| 5 | 17280 |
| 6 | 207360 |
| 7 | 2903040 |
| 8 | 43545600 |
| 9 | 696729600 |
| 10 | 12541132800 |
| 11 | 250822656000 |
| 12 | 5267275776000 |
| 13 | 115880067072000 |
| 14 | 2781121609728000 |
| 15 | 69528040243200000 |
| 16 | 1807729046323200000 |
| 17 | 48808684250726400000 |
| 18 | 1366643159020339200000 |
[1,4,24,192,1728,17280,207360,2903040,43545600, 696729600,12541132800,250822656000,5267275776000, 115880067072000,2781121609728000, 69528040243200000,1807729046323200000, 48808684250726400000,1366643159020339200000] |