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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 28 |
| 3 | 1552 |
| 4 | 4817152 |
| 5 | 46409906716672 |
| 6 | 4307758882900393634270543872 |
| 7 | 37113573186414494550922197215584520229965687291643953152 |
[1,4,28,1552,4817152,46409906716672, 4307758882900393634270543872, 37113573186414494550922197215584520229965687291643\ 953152] |