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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 26 |
| 5 | 138 |
| 6 | 1523 |
| 7 | 26489 |
| 8 | 687930 |
| 9 | 27990897 |
| 10 | 1765820801 |
| 11 | 172024403235 |
| 12 | 25959739501756 |
[1,1,4,26,138,1523,26489,687930,27990897, 1765820801,172024403235,25959739501756] |