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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 54 |
| 4 | 728 |
| 5 | 13000 |
| 6 | 290352 |
| 7 | 7800016 |
| 8 | 245115264 |
| 9 | 8826560640 |
| 10 | 358463525120 |
| 11 | 16212238054144 |
| 12 | 808215885708288 |
| 13 | 44035925223746560 |
| 14 | 2603618739995621376 |
| 15 | 166031767704180111360 |
| 16 | 11359670347331723952128 |
| 17 | 830065763154102656204800 |
| 18 | 64518486557995327748898816 |
[1,1,6,54,728,13000,290352,7800016,245115264, 8826560640,358463525120,16212238054144, 808215885708288,44035925223746560, 2603618739995621376,166031767704180111360, 11359670347331723952128,830065763154102656204800, 64518486557995327748898816] |