The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 5 |
| 3 | 15 |
| 4 | 32 |
| 5 | 90 |
| 6 | 189 |
| 7 | 527 |
| 8 | 1104 |
| 9 | 3074 |
| 10 | 6437 |
| 11 | 17919 |
| 12 | 37520 |
| 13 | 104442 |
| 14 | 218685 |
| 15 | 608735 |
| 16 | 1274592 |
| 17 | 3547970 |
| 18 | 7428869 |
| 19 | 20679087 |
| 20 | 43298624 |
| 21 | 120526554 |
| 22 | 252362877 |
| 23 | 702480239 |
| 24 | 1470878640 |
| 25 | 4094354882 |
| 26 | 8572908965 |
| 27 | 23863649055 |
| 28 | 49966575152 |
[0,2,5,15,32,90,189,527,1104,3074,6437,17919, 37520,104442,218685,608735,1274592,3547970, 7428869,20679087,43298624,120526554,252362877, 702480239,1470878640,4094354882,8572908965, 23863649055,49966575152] |