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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 9 |
| 4 | 27 |
| 5 | 81 |
| 6 | 240 |
| 7 | 711 |
| 8 | 2094 |
| 9 | 6152 |
| 10 | 18012 |
| 11 | 52613 |
| 12 | 153297 |
| 13 | 445772 |
| 14 | 1293780 |
| 15 | 3748820 |
| 16 | 10845935 |
| 17 | 31336532 |
| 18 | 90426198 |
| 19 | 260644262 |
| 20 | 750502831 |
| 21 | 2158961013 |
| 22 | 6205225334 |
| 23 | 17820505454 |
| 24 | 51139664497 |
| 25 | 146654181925 |
| 26 | 420291420558 |
[0,1,3,9,27,81,240,711,2094,6152,18012,52613, 153297,445772,1293780,3748820,10845935,31336532, 90426198,260644262,750502831,2158961013, 6205225334,17820505454,51139664497,146654181925, 420291420558] |