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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 40 |
| 4 | 296 |
| 5 | 2400 |
| 6 | 20928 |
| 7 | 192768 |
| 8 | 1848960 |
| 9 | 18277888 |
| 10 | 184890368 |
| 11 | 1904259072 |
| 12 | 19898765312 |
| 13 | 210424545280 |
| 14 | 2247494172672 |
| 15 | 24209586782208 |
| 16 | 262696649785344 |
| 17 | 2868744309571584 |
| 18 | 31504024885002240 |
| 19 | 347697247933169664 |
[0,1,6,40,296,2400,20928,192768,1848960,18277888, 184890368,1904259072,19898765312,210424545280, 2247494172672,24209586782208,262696649785344, 2868744309571584,31504024885002240, 347697247933169664] |