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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 9 |
| 5 | 41 |
| 6 | 121 |
| 7 | 2241 |
| 8 | 18481 |
| 9 | 91729 |
| 10 | 2577681 |
| 11 | 30833441 |
| 12 | 215554681 |
| 13 | 8126363961 |
| 14 | 127462383049 |
| 15 | 1150296157921 |
| 16 | 54416525377761 |
| 17 | 1056352067669921 |
| 18 | 11684649751431841 |
| 19 | 665061201610232769 |
| 20 | 15390714465319910761 |
| 21 | 201615391902487799881 |
[1,1,1,1,9,41,121,2241,18481,91729,2577681, 30833441,215554681,8126363961,127462383049, 1150296157921,54416525377761,1056352067669921, 11684649751431841,665061201610232769, 15390714465319910761,201615391902487799881] |