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| n | a(n) |
|---|---|
| 2 | 12 |
| 3 | 48 |
| 4 | 180 |
| 5 | 792 |
| 6 | 3444 |
| 7 | 15000 |
| 8 | 64932 |
| 9 | 280200 |
| 10 | 1204572 |
| 11 | 5159448 |
| 12 | 22043292 |
| 13 | 93952428 |
| 14 | 399711348 |
| 15 | 1697721852 |
| 16 | 7200873444 |
| 17 | 30500477676 |
| 18 | 129049335924 |
| 19 | 545436439536 |
| 20 | 2303305856916 |
[12,48,180,792,3444,15000,64932,280200,1204572, 5159448,22043292,93952428,399711348,1697721852, 7200873444,30500477676,129049335924,545436439536, 2303305856916] |