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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 100 |
| 6 | 360 |
| 7 | 1274 |
| 8 | 4368 |
| 9 | 14760 |
| 10 | 49200 |
| 11 | 162382 |
| 12 | 531432 |
| 13 | 1727180 |
| 14 | 5580120 |
| 15 | 17936130 |
| 16 | 57395616 |
| 17 | 182948560 |
| 18 | 581130720 |
| 19 | 1840247318 |
| 20 | 5811307320 |
| 21 | 18305618100 |
| 22 | 57531942600 |
| 23 | 180441092746 |
| 24 | 564859072944 |
| 25 | 1765184603000 |
| 26 | 5507375961360 |
| 27 | 17157594341214 |
| 28 | 53379182394888 |
[0,0,0,6,24,100,360,1274,4368,14760,49200,162382, 531432,1727180,5580120,17936130,57395616, 182948560,581130720,1840247318,5811307320, 18305618100,57531942600,180441092746,564859072944, 1765184603000,5507375961360,17157594341214, 53379182394888] |