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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 20 |
| 5 | 408 |
| 6 | 2249424 |
| 7 | 1098000299233152 |
| 8 | 1361974282591521291068503774196960256 |
[1,1,2,20,408,2249424,1098000299233152, 1361974282591521291068503774196960256] |