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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 1 |
| 2 | 7 |
| 3 | 25 |
| 4 | 87 |
| 5 | 329 |
| 6 | 1359 |
| 7 | 6001 |
| 8 | 27759 |
| 9 | 132689 |
| 10 | 649815 |
| 11 | 3242377 |
| 12 | 16421831 |
| 13 | 84196761 |
| 14 | 436129183 |
| 15 | 2278835681 |
| 16 | 11996748255 |
| 17 | 63568974241 |
| 18 | 338777252263 |
| 19 | 1814623238137 |
| 20 | 9763917858359 |
| 21 | 52750451120361 |
| 22 | 286036294786287 |
| 23 | 1556185889290065 |
| 24 | 8492182185653327 |
| 25 | 46471113779766769 |
[-1,1,7,25,87,329,1359,6001,27759,132689,649815, 3242377,16421831,84196761,436129183,2278835681, 11996748255,63568974241,338777252263, 1814623238137,9763917858359,52750451120361, 286036294786287,1556185889290065,8492182185653327, 46471113779766769] |