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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 56 |
| 5 | 897 |
| 6 | 20932 |
| 7 | 930123 |
| 8 | 73484449 |
| 9 | 11082127004 |
| 10 | 2811843090472 |
[1,4,13,56,897,20932,930123,73484449,11082127004, 2811843090472] |