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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 18 |
| 3 | 104994 |
| 4 | 121522844381309386290 |
| 5 | 218087967243211343601293080693944220009283482715374120407628181429351990598196290 |
[1,2,18,104994,121522844381309386290, 21808796724321134360129308069394422000928348271537\ 4120407628181429351990598196290] |