| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 7 |
| 5 | 18 |
| 6 | 80 |
| 7 | 284 |
| 8 | 1169 |
| 9 | 4628 |
| 10 | 19137 |
| 11 | 79165 |
| 12 | 333058 |
| 13 | 1410608 |
| 14 | 6029816 |
| 15 | 25941384 |
| 16 | 112315945 |
| 17 | 488862888 |
| 18 | 2138161043 |
| 19 | 9391903131 |
| 20 | 41414729419 |
| 21 | 183264846010 |
| 22 | 813564012660 |
| 23 | 3622193670040 |
| 24 | 16170171489820 |
| 25 | 72364908958800 |
| 26 | 324586284275500 |
| 27 | 1458976377988636 |
[0,1,1,7,18,80,284,1169,4628,19137,79165,333058, 1410608,6029816,25941384,112315945,488862888, 2138161043,9391903131,41414729419,183264846010, 813564012660,3622193670040,16170171489820, 72364908958800,324586284275500,1458976377988636] |