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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 324 |
| 3 | 6572 |
| 4 | 132640 |
| 5 | 3030492 |
| 6 | 68633066 |
| 7 | 1733220521 |
| 8 | 43321058602 |
| 9 | 1182486223832 |
[1,18,324,6572,132640,3030492,68633066,1733220521, 43321058602,1182486223832] |