| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 9 |
| 6 | 50 |
| 7 | 318 |
| 8 | 2310 |
| 9 | 19060 |
| 10 | 176310 |
| 11 | 1807181 |
| 12 | 20330788 |
| 13 | 249052161 |
| 14 | 3299941145 |
| 15 | 47024161317 |
| 16 | 717118460090 |
| 17 | 11653174976468 |
| 18 | 201017268344078 |
| 19 | 3668565147279423 |
| 20 | 70619879085128903 |
| 21 | 1430052551473860292 |
[1,0,0,0,2,9,50,318,2310,19060,176310,1807181, 20330788,249052161,3299941145,47024161317, 717118460090,11653174976468,201017268344078, 3668565147279423,70619879085128903, 1430052551473860292] |