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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 65 |
| 6 | 241 |
| 7 | 889 |
| 8 | 3472 |
| 9 | 13622 |
| 10 | 55340 |
| 11 | 225557 |
| 12 | 940725 |
| 13 | 3937330 |
| 14 | 16738031 |
| 15 | 71404967 |
| 16 | 307999065 |
| 17 | 1332931401 |
| 18 | 5815439839 |
| 19 | 25450058722 |
| 20 | 112060278048 |
| 21 | 494798567807 |
| 22 | 2195172975521 |
| 23 | 9763509301815 |
| 24 | 43589884062136 |
| 25 | 195052842541424 |
| 26 | 875498008541850 |
| 27 | 3937713690439906 |
| 28 | 17755851945737789 |
[1,1,2,6,20,65,241,889,3472,13622,55340,225557, 940725,3937330,16738031,71404967,307999065, 1332931401,5815439839,25450058722,112060278048, 494798567807,2195172975521,9763509301815, 43589884062136,195052842541424,875498008541850, 3937713690439906,17755851945737789] |