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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 5 |
| 3 | 15 |
| 4 | 845 |
| 5 | 403227665 |
| 6 | 64175114443109790962237345 |
| 7 | 264288160993294964501375691029638701718807009656135518176301450923295365341665 |
[4,5,15,845,403227665,64175114443109790962237345, 26428816099329496450137569102963870171880700965613\ 5518176301450923295365341665] |