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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 8 |
| 3 | 61 |
| 4 | 480 |
| 5 | 3881 |
| 6 | 31976 |
| 7 | 266981 |
| 8 | 2251136 |
| 9 | 19124881 |
| 10 | 163452168 |
| 11 | 1403748941 |
| 12 | 12104113632 |
| 13 | 104723793721 |
| 14 | 908680775528 |
| 15 | 7904234296181 |
| 16 | 68905275700736 |
| 17 | 601832985410081 |
| 18 | 5265459181363976 |
| 19 | 46137526574521181 |
| 20 | 404821208100919520 |
| 21 | 3556361565584509001 |
[0,1,8,61,480,3881,31976,266981,2251136,19124881, 163452168,1403748941,12104113632,104723793721, 908680775528,7904234296181,68905275700736, 601832985410081,5265459181363976, 46137526574521181,404821208100919520, 3556361565584509001] |