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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 6 |
| 3 | 9 |
| 4 | 168 |
| 5 | 810 |
| 6 | 11592 |
| 7 | 103320 |
| 8 | 1511808 |
| 9 | 19350576 |
| 10 | 315908640 |
| 11 | 5127930720 |
| 12 | 95386497984 |
| 13 | 1843728194880 |
| 14 | 38978317929600 |
| 15 | 866801578406400 |
| 16 | 20627303078937600 |
| 17 | 516780346452733440 |
| 18 | 13695223899883530240 |
| 19 | 381043219813390540800 |
| 20 | 11135125489382277811200 |
[1,0,6,9,168,810,11592,103320,1511808,19350576, 315908640,5127930720,95386497984,1843728194880, 38978317929600,866801578406400,20627303078937600, 516780346452733440,13695223899883530240, 381043219813390540800,11135125489382277811200] |