The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 23 |
| 6 | 63 |
| 7 | 155 |
| 8 | 448 |
| 9 | 1152 |
| 10 | 3452 |
| 11 | 9158 |
| 12 | 28177 |
| 13 | 76537 |
| 14 | 240343 |
| 15 | 665073 |
| 16 | 2122968 |
| 17 | 5963685 |
| 18 | 19295541 |
| 19 | 54883588 |
| 20 | 179608831 |
[1,1,2,4,10,23,63,155,448,1152,3452,9158,28177, 76537,240343,665073,2122968,5963685,19295541, 54883588,179608831] |