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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 31 |
| 4 | 460 |
| 5 | 12076 |
| 6 | 420336 |
| 7 | 21114864 |
| 8 | 1325949696 |
| 9 | 109027627776 |
| 10 | 10771080883200 |
| 11 | 1316468976307200 |
| 12 | 187978181665996800 |
| 13 | 31997755234356019200 |
| 14 | 6232784237890147123200 |
| 15 | 1409976507981835100160000 |
| 16 | 359243973790625586216960000 |
| 17 | 104259271562188189469245440000 |
[0,1,3,31,460,12076,420336,21114864,1325949696, 109027627776,10771080883200,1316468976307200, 187978181665996800,31997755234356019200, 6232784237890147123200,1409976507981835100160000, 359243973790625586216960000, 104259271562188189469245440000] |