The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 14 |
| 4 | 40 |
| 5 | 96 |
| 6 | 268 |
| 7 | 664 |
| 8 | 1820 |
| 9 | 4588 |
| 10 | 12464 |
| 11 | 31712 |
| 12 | 85704 |
| 13 | 219376 |
| 14 | 590640 |
| 15 | 1518652 |
| 16 | 4077112 |
| 17 | 10518364 |
| 18 | 28177388 |
| 19 | 72883016 |
| 20 | 194910964 |
| 21 | 505202708 |
| 22 | 1349189968 |
| 23 | 3503014492 |
| 24 | 9344407884 |
| 25 | 24296044256 |
| 26 | 64748290040 |
| 27 | 168550939272 |
[1,2,6,14,40,96,268,664,1820,4588,12464,31712, 85704,219376,590640,1518652,4077112,10518364, 28177388,72883016,194910964,505202708,1349189968, 3503014492,9344407884,24296044256,64748290040, 168550939272] |