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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 69 |
| 5 | 241 |
| 6 | 846 |
| 7 | 2977 |
| 8 | 10490 |
| 9 | 36994 |
| 10 | 130532 |
| 11 | 460737 |
| 12 | 1626629 |
| 13 | 5743674 |
| 14 | 20283121 |
| 15 | 71632290 |
| 16 | 252989326 |
| 17 | 893528468 |
| 18 | 3155899165 |
| 19 | 11146628105 |
| 20 | 39370204614 |
| 21 | 139057473905 |
| 22 | 491159630010 |
| 23 | 1734810719530 |
| 24 | 6127485120996 |
[1,2,6,20,69,241,846,2977,10490,36994,130532, 460737,1626629,5743674,20283121,71632290, 252989326,893528468,3155899165,11146628105, 39370204614,139057473905,491159630010, 1734810719530,6127485120996] |