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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 35 |
| 5 | 220 |
| 6 | 1622 |
| 7 | 13480 |
| 8 | 123212 |
| 9 | 1218694 |
| 10 | 12898292 |
| 11 | 144890911 |
| 12 | 1717072304 |
| 13 | 21367220392 |
| 14 | 278174617499 |
| 15 | 3777454890226 |
| 16 | 53372573914742 |
| 17 | 783004637781214 |
| 18 | 11905653060557285 |
| 19 | 187325244287570431 |
| 20 | 3045651218248945454 |
| 21 | 51103551998888439679 |
| 22 | 883901254149820933025 |
[1,1,2,7,35,220,1622,13480,123212,1218694, 12898292,144890911,1717072304,21367220392, 278174617499,3777454890226,53372573914742, 783004637781214,11905653060557285, 187325244287570431,3045651218248945454, 51103551998888439679,883901254149820933025] |