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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 6 |
| 3 | 28 |
| 4 | 165 |
| 5 | 1092 |
| 6 | 7752 |
| 7 | 57684 |
| 8 | 444015 |
| 9 | 3506100 |
| 10 | 28242984 |
| 11 | 231180144 |
| 12 | 1917334783 |
[3,6,28,165,1092,7752,57684,444015,3506100, 28242984,231180144,1917334783] |