| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 15 |
| 4 | 42 |
| 5 | 116 |
| 6 | 330 |
| 7 | 951 |
| 8 | 2778 |
| 9 | 8180 |
| 10 | 24234 |
| 11 | 72087 |
| 12 | 215034 |
| 13 | 642644 |
| 14 | 1923018 |
| 15 | 5759223 |
| 16 | 17258010 |
| 17 | 51734708 |
| 18 | 155125482 |
| 19 | 465219159 |
| 20 | 1395342906 |
| 21 | 4185399572 |
| 22 | 12554940426 |
| 23 | 37662304695 |
| 24 | 112981880922 |
| 25 | 338935576436 |
| 26 | 1016786596650 |
| 27 | 3050319524631 |
| 28 | 9150878043258 |
[1,2,6,15,42,116,330,951,2778,8180,24234,72087, 215034,642644,1923018,5759223,17258010,51734708, 155125482,465219159,1395342906,4185399572, 12554940426,37662304695,112981880922,338935576436, 1016786596650,3050319524631,9150878043258] |