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 | 13 |
| 5 | 33 |
| 6 | 123 |
| 7 | 366 |
| 8 | 1468 |
| 9 | 4743 |
| 10 | 19935 |
| 11 | 68259 |
| 12 | 296270 |
| 13 | 1059045 |
| 14 | 4703653 |
| 15 | 17371257 |
| 16 | 78488374 |
| 17 | 297384019 |
| 18 | 1361456225 |
| 19 | 5266059738 |
| 20 | 24359357814 |
| 21 | 95838621697 |
| 22 | 447027183728 |
| 23 | 1784055744603 |
| 24 | 8378335209695 |
| 25 | 33846086058778 |
| 26 | 159849556940540 |
| 27 | 652542059175631 |
| 28 | 3096521590494683 |
[1,1,2,4,13,33,123,366,1468,4743,19935,68259, 296270,1059045,4703653,17371257,78488374, 297384019,1361456225,5266059738,24359357814, 95838621697,447027183728,1784055744603, 8378335209695,33846086058778,159849556940540, 652542059175631,3096521590494683] |