The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 56 |
| 4 | 208 |
| 5 | 773 |
| 6 | 2872 |
| 7 | 10672 |
| 8 | 39655 |
| 9 | 147350 |
| 10 | 547523 |
| 11 | 2034486 |
| 12 | 7559742 |
| 13 | 28090486 |
| 14 | 104378617 |
| 15 | 387850022 |
| 16 | 1441172953 |
| 17 | 5355109869 |
| 18 | 19898515060 |
| 19 | 73938894118 |
| 20 | 274742112508 |
| 21 | 1020886629235 |
| 22 | 3793410119173 |
| 23 | 14095551768590 |
[1,4,15,56,208,773,2872,10672,39655,147350,547523, 2034486,7559742,28090486,104378617,387850022, 1441172953,5355109869,19898515060,73938894118, 274742112508,1020886629235,3793410119173, 14095551768590] |