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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 13 |
| 4 | 52 |
| 5 | 261 |
| 6 | 1567 |
| 7 | 10970 |
| 8 | 87761 |
| 9 | 789855 |
| 10 | 7898554 |
| 11 | 86884101 |
| 12 | 1042609219 |
| 13 | 13553919858 |
| 14 | 189754878021 |
| 15 | 2846323170326 |
| 16 | 45541170725230 |
| 17 | 774199902328924 |
| 18 | 13935598241920639 |
| 19 | 264776366596492150 |
| 20 | 5295527331929843000 |
[2,4,13,52,261,1567,10970,87761,789855,7898554, 86884101,1042609219,13553919858,189754878021, 2846323170326,45541170725230,774199902328924, 13935598241920639,264776366596492150, 5295527331929843000] |