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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 5 |
| 2 | 21 |
| 3 | 51 |
| 4 | 170 |
| 5 | 454 |
| 6 | 1367 |
| 7 | 3776 |
| 8 | 11062 |
| 9 | 31054 |
| 10 | 89935 |
| 11 | 254654 |
| 12 | 733725 |
| 13 | 2088612 |
| 14 | 6004175 |
| 15 | 17150397 |
| 16 | 49267851 |
| 17 | 141065942 |
| 18 | 405274932 |
| 19 | 1162440833 |
| 20 | 3341173303 |
| 21 | 9596468129 |
| 22 | 27600014912 |
| 23 | 79359955225 |
| 24 | 228397685542 |
| 25 | 657335642733 |
| 26 | 1893081845674 |
| 27 | 5452722985712 |
[2,5,21,51,170,454,1367,3776,11062,31054,89935, 254654,733725,2088612,6004175,17150397,49267851, 141065942,405274932,1162440833,3341173303, 9596468129,27600014912,79359955225,228397685542, 657335642733,1893081845674,5452722985712] |