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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 110 |
| 5 | 540 |
| 6 | 2772 |
| 7 | 14704 |
| 8 | 79974 |
| 9 | 443594 |
| 10 | 2499640 |
| 11 | 14269320 |
| 12 | 82346004 |
| 13 | 479604748 |
| 14 | 2815557264 |
| 15 | 16643093712 |
| 16 | 98974828886 |
| 17 | 591742372068 |
| 18 | 3554708076858 |
| 19 | 21444913596408 |
| 20 | 129870710693976 |
| 21 | 789237890852160 |
| 22 | 4811481299622276 |
| 23 | 29417496447990096 |
| 24 | 180337119342194820 |
[1,2,6,24,110,540,2772,14704,79974,443594,2499640, 14269320,82346004,479604748,2815557264, 16643093712,98974828886,591742372068, 3554708076858,21444913596408,129870710693976, 789237890852160,4811481299622276, 29417496447990096,180337119342194820] |