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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 78 |
| 5 | 294 |
| 6 | 1232 |
| 7 | 5054 |
| 8 | 21840 |
| 9 | 94060 |
| 10 | 414734 |
| 11 | 1841452 |
| 12 | 8258804 |
| 13 | 37354536 |
| 14 | 169989700 |
| 15 | 778394626 |
| 16 | 3584284230 |
| 17 | 16570124008 |
| 18 | 76984172720 |
| 19 | 358776753034 |
| 20 | 1678242178310 |
| 21 | 7874377974572 |
| 22 | 37042326513184 |
| 23 | 174754402790452 |
| 24 | 826160373343962 |
| 25 | 3914741263937712 |
| 26 | 18587462489170296 |
| 27 | 88408330271653002 |
[1,2,6,20,78,294,1232,5054,21840,94060,414734, 1841452,8258804,37354536,169989700,778394626, 3584284230,16570124008,76984172720,358776753034, 1678242178310,7874377974572,37042326513184, 174754402790452,826160373343962,3914741263937712, 18587462489170296,88408330271653002] |