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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 3 |
| 3 | 12 |
| 4 | 57 |
| 5 | 300 |
| 6 | 1686 |
| 7 | 9912 |
| 8 | 60213 |
| 9 | 374988 |
| 10 | 2381322 |
| 11 | 15361896 |
| 12 | 100389306 |
| 13 | 663180024 |
| 14 | 4421490924 |
| 15 | 29712558576 |
| 16 | 201046204173 |
| 17 | 1368578002188 |
| 18 | 9366084668802 |
| 19 | 64403308499592 |
| 20 | 444739795023054 |
| 21 | 3082969991029800 |
[2,3,12,57,300,1686,9912,60213,374988,2381322, 15361896,100389306,663180024,4421490924, 29712558576,201046204173,1368578002188, 9366084668802,64403308499592,444739795023054, 3082969991029800] |