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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 23 |
| 3 | 181 |
| 4 | 1889 |
| 5 | 25411 |
| 6 | 427615 |
| 7 | 8736337 |
| 8 | 210911489 |
| 9 | 5882285971 |
| 10 | 186121646831 |
| 11 | 6585885144697 |
| 12 | 257640988064641 |
| 13 | 11039620794801691 |
| 14 | 514147575711741119 |
| 15 | 25858553659455655201 |
| 16 | 1396703647943164718081 |
| 17 | 80633376290492591578147 |
| 18 | 4954794080385073122030799 |
[1,4,23,181,1889,25411,427615,8736337,210911489, 5882285971,186121646831,6585885144697, 257640988064641,11039620794801691, 514147575711741119,25858553659455655201, 1396703647943164718081,80633376290492591578147, 4954794080385073122030799] |