| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 8 |
| 3 | 21 |
| 4 | 56 |
| 5 | 145 |
| 6 | 366 |
| 7 | 945 |
| 8 | 2506 |
| 9 | 6633 |
| 10 | 17776 |
| 11 | 48521 |
| 12 | 133106 |
| 13 | 369019 |
| 14 | 1028404 |
| 15 | 2880287 |
| 16 | 8100948 |
| 17 | 22877145 |
| 18 | 64823568 |
| 19 | 184274931 |
| 20 | 525282740 |
| 21 | 1501215193 |
| 22 | 4299836186 |
| 23 | 12340952049 |
| 24 | 35486796312 |
| 25 | 102220582465 |
| 26 | 294917666854 |
| 27 | 852123981581 |
| 28 | 2465458792768 |
[0,3,8,21,56,145,366,945,2506,6633,17776,48521, 133106,369019,1028404,2880287,8100948,22877145, 64823568,184274931,525282740,1501215193, 4299836186,12340952049,35486796312,102220582465, 294917666854,852123981581,2465458792768] |