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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 78 |
| 5 | 288 |
| 6 | 1220 |
| 7 | 4840 |
| 8 | 21364 |
| 9 | 87936 |
| 10 | 398228 |
| 11 | 1682880 |
| 12 | 7759528 |
| 13 | 33369292 |
| 14 | 155811592 |
| 15 | 679381856 |
| 16 | 3203272984 |
| 17 | 14110245460 |
| 18 | 67023556416 |
| 19 | 297748804696 |
| 20 | 1422910658272 |
| 21 | 6363423616772 |
| 22 | 30557750895420 |
| 23 | 137442151034588 |
| 24 | 662730771093360 |
| 25 | 2994811386918788 |
| 26 | 14489809853564064 |
| 27 | 65748135236212348 |
[1,2,6,20,78,288,1220,4840,21364,87936,398228, 1682880,7759528,33369292,155811592,679381856, 3203272984,14110245460,67023556416,297748804696, 1422910658272,6363423616772,30557750895420, 137442151034588,662730771093360,2994811386918788, 14489809853564064,65748135236212348] |