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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 32 |
| 5 | 392 |
| 6 | 6492 |
| 7 | 135876 |
| 8 | 3450048 |
| 9 | 103437240 |
| 10 | 3592136052 |
| 11 | 142420085352 |
| 12 | 6373515782544 |
| 13 | 318952925294496 |
| 14 | 17709716546754768 |
| 15 | 1083721599571837632 |
| 16 | 72661988008040494752 |
| 17 | 5310638869813310865984 |
| 18 | 421165309915181979699168 |
| 19 | 36095229917026934599948992 |
[1,1,4,32,392,6492,135876,3450048,103437240, 3592136052,142420085352,6373515782544, 318952925294496,17709716546754768, 1083721599571837632,72661988008040494752, 5310638869813310865984,421165309915181979699168, 36095229917026934599948992] |