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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 18 |
| 5 | 181 |
| 6 | 2792 |
| 7 | 62960 |
| 8 | 2020256 |
| 9 | 90847421 |
| 10 | 5674075324 |
| 11 | 489320844468 |
| 12 | 57995151443168 |
[1,1,1,3,18,181,2792,62960,2020256,90847421, 5674075324,489320844468,57995151443168] |