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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 4 |
| 2 | 20 |
| 3 | 312 |
| 4 | 67272 |
| 5 | 4295632512 |
| 6 | 18446744138139694080 |
| 7 | 340282366920938463850756233731336688000 |
| 8 | 115792089237316195423570985008687907862797890939426841022371924616155698285440 |
[2,4,20,312,67272,4295632512,18446744138139694080, 340282366920938463850756233731336688000, 11579208923731619542357098500868790786279789093942\ 6841022371924616155698285440] |