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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 9 |
| 3 | 40 |
| 4 | 192 |
| 5 | 993 |
| 6 | 5375 |
| 7 | 30081 |
| 8 | 172650 |
| 9 | 1010640 |
| 10 | 6010530 |
| 11 | 36214656 |
| 12 | 220590082 |
| 13 | 1356131892 |
| 14 | 8403647454 |
| 15 | 52436122717 |
| 16 | 329170499604 |
| 17 | 2077465903503 |
| 18 | 13173914483799 |
| 19 | 83897445169341 |
| 20 | 536355204428412 |
| 21 | 3440875097256529 |
| 22 | 22144300030907667 |
[1,3,9,40,192,993,5375,30081,172650,1010640, 6010530,36214656,220590082,1356131892,8403647454, 52436122717,329170499604,2077465903503, 13173914483799,83897445169341,536355204428412, 3440875097256529,22144300030907667] |