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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 10 |
| 4 | 70 |
| 5 | 530 |
| 6 | 4278 |
| 7 | 36050 |
| 8 | 313558 |
| 9 | 2793970 |
| 10 | 25374262 |
| 11 | 234016530 |
| 12 | 2185799958 |
| 13 | 20634634930 |
| 14 | 196569384566 |
| 15 | 1887215137490 |
| 16 | 18242042039894 |
| 17 | 177383206638450 |
| 18 | 1733967807665334 |
| 19 | 17029818475966610 |
| 20 | 167961197068279190 |
[1,0,2,10,70,530,4278,36050,313558,2793970, 25374262,234016530,2185799958,20634634930, 196569384566,1887215137490,18242042039894, 177383206638450,1733967807665334, 17029818475966610,167961197068279190] |