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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 220 |
| 3 | 1780 |
| 4 | 11282 |
| 5 | 59124 |
| 6 | 263702 |
| 7 | 1022668 |
| 8 | 3509204 |
| 9 | 10822028 |
| 10 | 30434152 |
[1,20,220,1780,11282,59124,263702,1022668,3509204, 10822028,30434152] |