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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 27 |
| 4 | 74 |
| 5 | 197 |
| 6 | 519 |
| 7 | 1362 |
| 8 | 3569 |
| 9 | 9347 |
| 10 | 24474 |
| 11 | 64077 |
| 12 | 167759 |
| 13 | 439202 |
| 14 | 1149849 |
| 15 | 3010347 |
| 16 | 7881194 |
| 17 | 20633237 |
| 18 | 54018519 |
| 19 | 141422322 |
| 20 | 370248449 |
| 21 | 969323027 |
| 22 | 2537720634 |
| 23 | 6643838877 |
| 24 | 17393795999 |
| 25 | 45537549122 |
| 26 | 119218851369 |
| 27 | 312119004987 |
| 28 | 817138163594 |
[-1,2,9,27,74,197,519,1362,3569,9347,24474,64077, 167759,439202,1149849,3010347,7881194,20633237, 54018519,141422322,370248449,969323027,2537720634, 6643838877,17393795999,45537549122,119218851369, 312119004987,817138163594] |