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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 34 |
| 3 | 432 |
| 4 | 7320 |
| 5 | 155040 |
| 6 | 3940560 |
| 7 | 116847360 |
| 8 | 3959786880 |
| 9 | 150965337600 |
| 10 | 6394994323200 |
| 11 | 297985937356800 |
| 12 | 15147464243788800 |
| 13 | 834153946904678400 |
| 14 | 49469459519031552000 |
| 15 | 3143339899991875584000 |
| 16 | 213046423884047609856000 |
[1,4,34,432,7320,155040,3940560,116847360, 3959786880,150965337600,6394994323200, 297985937356800,15147464243788800, 834153946904678400,49469459519031552000, 3143339899991875584000,213046423884047609856000] |