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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 19 |
| 5 | 127 |
| 6 | 985 |
| 7 | 8350 |
| 8 | 73675 |
| 9 | 664411 |
| 10 | 6078768 |
| 11 | 56198759 |
| 12 | 523924389 |
| 13 | 4918127659 |
[1,1,4,19,127,985,8350,73675,664411,6078768, 56198759,523924389,4918127659] |