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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 12 |
| 4 | 20 |
| 5 | 38 |
| 6 | 53 |
| 7 | 106 |
| 8 | 200 |
| 9 | 369 |
| 10 | 657 |
| 11 | 1227 |
| 12 | 2191 |
| 13 | 4268 |
| 14 | 8076 |
| 15 | 15291 |
| 16 | 28932 |
| 17 | 55125 |
| 18 | 105983 |
| 19 | 202482 |
| 20 | 391506 |
[2,6,12,20,38,53,106,200,369,657,1227,2191,4268, 8076,15291,28932,55125,105983,202482,391506] |