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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 7 |
| 5 | 17 |
| 6 | 49 |
| 7 | 145 |
| 8 | 415 |
| 9 | 1201 |
| 10 | 3473 |
| 11 | 10033 |
| 12 | 28999 |
| 13 | 83809 |
| 14 | 242209 |
| 15 | 700001 |
| 16 | 2023039 |
| 17 | 5846689 |
| 18 | 16897249 |
| 19 | 48833953 |
| 20 | 141132743 |
| 21 | 407881201 |
| 22 | 1178798545 |
| 23 | 3406791025 |
| 24 | 9845808799 |
| 25 | 28454915537 |
| 26 | 82236232177 |
| 27 | 237667122001 |
[-1,1,1,1,7,17,49,145,415,1201,3473,10033,28999, 83809,242209,700001,2023039,5846689,16897249, 48833953,141132743,407881201,1178798545, 3406791025,9845808799,28454915537,82236232177, 237667122001] |