| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 60 |
| 5 | 560 |
| 6 | 7350 |
| 7 | 111552 |
| 8 | 2009672 |
| 9 | 41378976 |
| 10 | 963527850 |
| 11 | 25009038560 |
| 12 | 716437784172 |
| 13 | 22453784964624 |
| 14 | 764345507271710 |
| 15 | 28085186967504240 |
| 16 | 1107971902218683280 |
| 17 | 46710909213378892352 |
| 18 | 2095883952368863510098 |
| 19 | 99724281567446320231104 |
| 20 | 5015524096516005263567540 |
[1,0,2,6,60,560,7350,111552,2009672,41378976, 963527850,25009038560,716437784172,22453784964624, 764345507271710,28085186967504240, 1107971902218683280,46710909213378892352, 2095883952368863510098,99724281567446320231104, 5015524096516005263567540] |