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| n | a(n) |
|---|---|
| 2 | 2 |
| 3 | 4 |
| 4 | 13 |
| 5 | 61 |
| 6 | 361 |
| 7 | 2521 |
| 8 | 20161 |
| 9 | 181441 |
| 10 | 1814401 |
| 11 | 19958401 |
| 12 | 239500801 |
| 13 | 3113510401 |
| 14 | 43589145601 |
| 15 | 653837184001 |
| 16 | 10461394944001 |
| 17 | 177843714048001 |
| 18 | 3201186852864001 |
| 19 | 60822550204416001 |
| 20 | 1216451004088320001 |
| 21 | 25545471085854720001 |
| 22 | 562000363888803840001 |
[2,4,13,61,361,2521,20161,181441,1814401,19958401, 239500801,3113510401,43589145601,653837184001, 10461394944001,177843714048001,3201186852864001, 60822550204416001,1216451004088320001, 25545471085854720001,562000363888803840001] |