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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 2 |
| 3 | 4 |
| 4 | 15 |
| 5 | 35 |
| 6 | 137 |
| 7 | 306 |
| 8 | 1056 |
| 9 | 2510 |
| 10 | 8094 |
| 11 | 21568 |
| 12 | 66310 |
| 13 | 183338 |
| 14 | 545993 |
| 15 | 1538831 |
[2,2,4,15,35,137,306,1056,2510,8094,21568,66310, 183338,545993,1538831] |