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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 32 |
| 5 | 240 |
| 6 | 2192 |
| 7 | 23856 |
| 8 | 303872 |
| 9 | 4427520 |
| 10 | 72545792 |
| 11 | 1320608256 |
| 12 | 26445350912 |
| 13 | 577722163200 |
| 14 | 13672510932992 |
| 15 | 348466876717056 |
| 16 | 9515645659185152 |
| 17 | 277168473987809280 |
| 18 | 8577847096804769792 |
| 19 | 281084141232170336256 |
| 20 | 9722444816080638574592 |
| 21 | 353990026542011001077760 |
[0,1,2,6,32,240,2192,23856,303872,4427520, 72545792,1320608256,26445350912,577722163200, 13672510932992,348466876717056,9515645659185152, 277168473987809280,8577847096804769792, 281084141232170336256,9722444816080638574592, 353990026542011001077760] |