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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 81 |
| 5 | 331 |
| 6 | 1408 |
| 7 | 6158 |
| 8 | 27500 |
| 9 | 124785 |
| 10 | 573374 |
| 11 | 2661181 |
| 12 | 12452537 |
| 13 | 58663693 |
| 14 | 277925301 |
| 15 | 1322985057 |
| 16 | 6323345510 |
| 17 | 30329047324 |
| 18 | 145911596929 |
| 19 | 703840378250 |
| 20 | 3403090924315 |
| 21 | 16488139150736 |
| 22 | 80033155681199 |
| 23 | 389120776564177 |
| 24 | 1894710889794849 |
| 25 | 9238112584833160 |
| 26 | 45097372279554299 |
| 27 | 220393971161197117 |
[1,2,6,21,81,331,1408,6158,27500,124785,573374, 2661181,12452537,58663693,277925301,1322985057, 6323345510,30329047324,145911596929,703840378250, 3403090924315,16488139150736,80033155681199, 389120776564177,1894710889794849,9238112584833160, 45097372279554299,220393971161197117] |