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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 80 |
| 5 | 303 |
| 6 | 847 |
| 7 | 3401 |
| 8 | 12816 |
| 9 | 47255 |
| 10 | 168306 |
| 11 | 628058 |
| 12 | 2243714 |
| 13 | 8741445 |
| 14 | 33079519 |
| 15 | 125266470 |
| 16 | 474015314 |
| 17 | 1806320048 |
| 18 | 6945673364 |
| 19 | 26539784794 |
| 20 | 102630867522 |
[2,6,24,80,303,847,3401,12816,47255,168306,628058, 2243714,8741445,33079519,125266470,474015314, 1806320048,6945673364,26539784794,102630867522] |