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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 54 |
| 4 | 756 |
| 5 | 14580 |
| 6 | 358668 |
| 7 | 10736712 |
| 8 | 378823392 |
| 9 | 15395255280 |
| 10 | 708217959600 |
| 11 | 36380741745744 |
| 12 | 2064234271203360 |
| 13 | 128214974795177088 |
| 14 | 8652900673357097472 |
| 15 | 630483717450225530880 |
| 16 | 49330027417316557012992 |
| 17 | 4124992361928178722764544 |
[0,1,6,54,756,14580,358668,10736712,378823392, 15395255280,708217959600,36380741745744, 2064234271203360,128214974795177088, 8652900673357097472,630483717450225530880, 49330027417316557012992,4124992361928178722764544] |