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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 13 |
| 4 | 47 |
| 5 | 107 |
| 6 | 643 |
| 7 | 1439 |
| 8 | 2879 |
| 9 | 34549 |
| 10 | 138197 |
| 11 | 858239 |
| 12 | 2029439 |
| 13 | 36449279 |
[2,4,13,47,107,643,1439,2879,34549,138197,858239, 2029439,36449279] |