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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 71 |
| 5 | 2403 |
| 6 | 238535 |
| 7 | 73506103 |
| 8 | 64732546521 |
| 9 | 189964969385932 |
| 10 | 1647943050926969975 |
[1,2,6,71,2403,238535,73506103,64732546521, 189964969385932,1647943050926969975] |