| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 4 |
| 2 | 9 |
| 3 | 23 |
| 4 | 55 |
| 5 | 126 |
| 6 | 293 |
| 7 | 680 |
| 8 | 1581 |
| 9 | 3676 |
| 10 | 8546 |
| 11 | 19867 |
| 12 | 46185 |
| 13 | 107367 |
| 14 | 249598 |
| 15 | 580245 |
| 16 | 1348906 |
| 17 | 3135826 |
| 18 | 7289911 |
| 19 | 16946987 |
| 20 | 39396965 |
| 21 | 91586832 |
| 22 | 212913553 |
| 23 | 494963960 |
| 24 | 1150651606 |
| 25 | 2674940451 |
| 26 | 6218482101 |
| 27 | 14456217007 |
| 28 | 33606627270 |
[2,4,9,23,55,126,293,680,1581,3676,8546,19867, 46185,107367,249598,580245,1348906,3135826, 7289911,16946987,39396965,91586832,212913553, 494963960,1150651606,2674940451,6218482101, 14456217007,33606627270] |