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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 22 |
| 4 | 162 |
| 5 | 1202 |
| 6 | 8974 |
| 7 | 66990 |
| 8 | 500018 |
| 9 | 3732178 |
| 10 | 27857358 |
| 11 | 207930158 |
| 12 | 1552011826 |
| 13 | 11584373970 |
| 14 | 86466944462 |
| 15 | 645398059822 |
| 16 | 4817316700722 |
| 17 | 35956941366482 |
| 18 | 268386264128974 |
| 19 | 2003262347565870 |
| 20 | 14952553724011058 |
| 21 | 111607380401824978 |
[0,2,22,162,1202,8974,66990,500018,3732178, 27857358,207930158,1552011826,11584373970, 86466944462,645398059822,4817316700722, 35956941366482,268386264128974,2003262347565870, 14952553724011058,111607380401824978] |