The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 20 |
| 3 | 201 |
| 4 | 1360 |
| 5 | 7001 |
| 6 | 29364 |
| 7 | 104881 |
| 8 | 329024 |
| 9 | 927441 |
| 10 | 2390004 |
| 11 | 5707449 |
| 12 | 12767184 |
| 13 | 26986089 |
| 14 | 54284244 |
| 15 | 104535009 |
| 16 | 193664256 |
| 17 | 346615329 |
| 18 | 601446996 |
| 19 | 1014889769 |
| 20 | 1669752016 |
| 21 | 2684641785 |
| 22 | 4226553716 |
| 23 | 6526963345 |
| 24 | 9902174016 |
| 25 | 14778775025 |
| 26 | 21725194036 |
| 27 | 31490462745 |
[0,1,20,201,1360,7001,29364,104881,329024,927441, 2390004,5707449,12767184,26986089,54284244, 104535009,193664256,346615329,601446996, 1014889769,1669752016,2684641785,4226553716, 6526963345,9902174016,14778775025,21725194036, 31490462745] |