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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 103 |
| 5 | 508 |
| 6 | 2452 |
| 7 | 11929 |
| 8 | 57856 |
| 9 | 280930 |
| 10 | 1363495 |
| 11 | 6618856 |
| 12 | 32128024 |
| 13 | 155953777 |
| 14 | 757013548 |
| 15 | 3674624638 |
| 16 | 17836995847 |
| 17 | 86582609284 |
| 18 | 420280790476 |
| 19 | 2040085854985 |
| 20 | 9902784679240 |
| 21 | 48069126732586 |
| 22 | 233332442310919 |
[0,1,4,22,103,508,2452,11929,57856,280930,1363495, 6618856,32128024,155953777,757013548,3674624638, 17836995847,86582609284,420280790476, 2040085854985,9902784679240,48069126732586, 233332442310919] |