The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 17 |
| 4 | 80 |
| 5 | 424 |
| 6 | 2744 |
| 7 | 19928 |
| 8 | 166984 |
| 9 | 1543176 |
| 10 | 15939792 |
| 11 | 178966512 |
| 12 | 2200820544 |
| 13 | 29089668672 |
| 14 | 415261531008 |
| 15 | 6316101256320 |
| 16 | 102692213061120 |
| 17 | 1766690411927040 |
| 18 | 32235156493470720 |
| 19 | 618870347081671680 |
| 20 | 12523381062124032000 |
| 21 | 265423904312781312000 |
[1,5,17,80,424,2744,19928,166984,1543176,15939792, 178966512,2200820544,29089668672,415261531008, 6316101256320,102692213061120,1766690411927040, 32235156493470720,618870347081671680, 12523381062124032000,265423904312781312000] |