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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 15 |
| 3 | 4140 |
| 4 | 10480142147 |
| 5 | 128064670049908713818925644 |
| 6 | 172134143357358850934369963665272571125557575184049758045339873395 |
[1,2,15,4140,10480142147, 128064670049908713818925644, 17213414335735885093436996366527257112555757518404\ 9758045339873395] |