| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 6 |
| 2 | 456 |
| 3 | 6240 |
| 4 | 131238 |
| 5 | 2238780 |
| 6 | 41011296 |
| 7 | 730283034 |
| 8 | 13143304440 |
| 9 | 235581102912 |
| 10 | 4229156006790 |
| 11 | 75876624195564 |
| 12 | 1361636473680576 |
| 13 | 24432987781993530 |
| 14 | 438436202143461288 |
| 15 | 7867390833380267040 |
| 16 | 141174789462751501926 |
| 17 | 2533277512666920359964 |
[0,6,456,6240,131238,2238780,41011296,730283034, 13143304440,235581102912,4229156006790, 75876624195564,1361636473680576,24432987781993530, 438436202143461288,7867390833380267040, 141174789462751501926,2533277512666920359964] |