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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 277 |
| 6 | 1109 |
| 7 | 4578 |
| 8 | 19276 |
| 9 | 82614 |
| 10 | 359661 |
| 11 | 1586055 |
| 12 | 7067002 |
| 13 | 31747505 |
| 14 | 143674019 |
| 15 | 654614385 |
| 16 | 3000538614 |
| 17 | 13824229597 |
| 18 | 63972253270 |
| 19 | 297222305536 |
| 20 | 1386101998356 |
| 21 | 6486263136848 |
| 22 | 30444998558904 |
| 23 | 143290472592821 |
| 24 | 676097366037068 |
| 25 | 3197627671498764 |
| 26 | 15156589256904697 |
| 27 | 71985821847295508 |
[1,2,6,20,72,277,1109,4578,19276,82614,359661, 1586055,7067002,31747505,143674019,654614385, 3000538614,13824229597,63972253270,297222305536, 1386101998356,6486263136848,30444998558904, 143290472592821,676097366037068,3197627671498764, 15156589256904697,71985821847295508] |