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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 40 |
| 5 | 295 |
| 6 | 2688 |
| 7 | 28588 |
| 8 | 348864 |
| 9 | 4802922 |
| 10 | 73652110 |
| 11 | 1245046836 |
| 12 | 23003289912 |
| 13 | 461188427544 |
| 14 | 9972307487660 |
| 15 | 231341792369010 |
| 16 | 5731422576446208 |
| 17 | 151032969213699536 |
| 18 | 4218265874407103640 |
| 19 | 124471244064061267032 |
| 20 | 3869361472890037713560 |
[1,0,2,6,40,295,2688,28588,348864,4802922, 73652110,1245046836,23003289912,461188427544, 9972307487660,231341792369010,5731422576446208, 151032969213699536,4218265874407103640, 124471244064061267032,3869361472890037713560] |