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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 19 |
| 5 | 61 |
| 6 | 197 |
| 7 | 640 |
| 8 | 2091 |
| 9 | 6860 |
| 10 | 22566 |
| 11 | 74365 |
| 12 | 245397 |
| 13 | 810639 |
| 14 | 2680025 |
| 15 | 8865866 |
[1,2,6,19,61,197,640,2091,6860,22566,74365,245397, 810639,2680025,8865866] |