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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 189 |
| 5 | 1941 |
| 6 | 28032 |
| 7 | 448157 |
| 8 | 8951313 |
| 9 | 194183520 |
| 10 | 4923018003 |
| 11 | 134463192215 |
[1,4,21,189,1941,28032,448157,8951313,194183520, 4923018003,134463192215] |