The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 23 |
| 6 | 53 |
| 7 | 182 |
| 8 | 599 |
| 9 | 1380 |
| 10 | 4739 |
| 11 | 15597 |
| 12 | 35933 |
| 13 | 123396 |
| 14 | 406121 |
| 15 | 935638 |
| 16 | 3213035 |
| 17 | 10574743 |
| 18 | 24362521 |
| 19 | 83662306 |
| 20 | 275349439 |
| 21 | 634361184 |
| 22 | 2178432991 |
| 23 | 7169660157 |
| 24 | 16517753305 |
| 25 | 56722920072 |
| 26 | 186686513521 |
| 27 | 430095947114 |
[0,1,2,7,23,53,182,599,1380,4739,15597,35933, 123396,406121,935638,3213035,10574743,24362521, 83662306,275349439,634361184,2178432991, 7169660157,16517753305,56722920072,186686513521, 430095947114] |