The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 9 |
| 3 | 22 |
| 4 | 54 |
| 5 | 123 |
| 6 | 281 |
| 7 | 618 |
| 8 | 1362 |
| 9 | 2934 |
| 10 | 6330 |
| 11 | 13452 |
| 12 | 28620 |
| 13 | 60243 |
| 14 | 126921 |
| 15 | 265282 |
| 16 | 554874 |
| 17 | 1153506 |
| 18 | 2399390 |
| 19 | 4966740 |
| 20 | 10286196 |
| 21 | 21219038 |
| 22 | 43790154 |
| 23 | 90076452 |
| 24 | 185353204 |
| 25 | 380364108 |
| 26 | 780786516 |
| 27 | 1599015192 |
| 28 | 3275589144 |
[1,3,9,22,54,123,281,618,1362,2934,6330,13452, 28620,60243,126921,265282,554874,1153506,2399390, 4966740,10286196,21219038,43790154,90076452, 185353204,380364108,780786516,1599015192, 3275589144] |