| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 5 |
| 5 | 17 |
| 6 | 90 |
| 7 | 542 |
| 8 | 3962 |
| 9 | 33554 |
| 10 | 324489 |
| 11 | 3520885 |
| 12 | 42300709 |
| 13 | 556530474 |
| 14 | 7945317484 |
| 15 | 122145525208 |
| 16 | 2008827010000 |
| 17 | 35143981009968 |
[1,0,1,1,5,17,90,542,3962,33554,324489,3520885, 42300709,556530474,7945317484,122145525208, 2008827010000,35143981009968] |