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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 13 |
| 3 | 37 |
| 4 | 97 |
| 5 | 241 |
| 6 | 577 |
| 7 | 1345 |
| 8 | 3073 |
| 9 | 6913 |
| 10 | 15361 |
| 11 | 33793 |
| 12 | 73729 |
| 13 | 159745 |
| 14 | 344065 |
| 15 | 737281 |
| 16 | 1572865 |
| 17 | 3342337 |
| 18 | 7077889 |
| 19 | 14942209 |
| 20 | 31457281 |
| 21 | 66060289 |
| 22 | 138412033 |
| 23 | 289406977 |
| 24 | 603979777 |
| 25 | 1258291201 |
| 26 | 2617245697 |
| 27 | 5435817985 |
[1,4,13,37,97,241,577,1345,3073,6913,15361,33793, 73729,159745,344065,737281,1572865,3342337, 7077889,14942209,31457281,66060289,138412033, 289406977,603979777,1258291201,2617245697, 5435817985] |