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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 2 |
| 2 | 4 |
| 3 | 18 |
| 4 | 648 |
| 5 | 3140062 |
| 6 | 503483766022188 |
| 7 | 171522187398423323340476473786538 |
[2,2,4,18,648,3140062,503483766022188, 171522187398423323340476473786538] |