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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 84 |
| 5 | 860 |
| 6 | 14430 |
| 7 | 257082 |
| 8 | 5678456 |
| 9 | 140241096 |
| 10 | 3952791450 |
| 11 | 123539438990 |
| 12 | 4266378769092 |
| 13 | 160943793753756 |
| 14 | 6592371152535350 |
| 15 | 291260465060881890 |
| 16 | 13809548247503299440 |
| 17 | 699362685890810753552 |
| 18 | 37679514498664685654706 |
[1,0,2,6,84,860,14430,257082,5678456,140241096, 3952791450,123539438990,4266378769092, 160943793753756,6592371152535350, 291260465060881890,13809548247503299440, 699362685890810753552,37679514498664685654706] |