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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 42 |
| 5 | 350 |
| 6 | 2450 |
| 7 | 16807 |
| 8 | 117306 |
| 9 | 823200 |
| 10 | 5767202 |
| 11 | 40356008 |
| 12 | 282458442 |
[0,2,6,42,350,2450,16807,117306,823200,5767202, 40356008,282458442] |