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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 8 |
| 3 | 35 |
| 4 | 266 |
| 5 | 1680 |
| 6 | 12804 |
| 7 | 93093 |
| 8 | 726440 |
| 9 | 5635058 |
| 10 | 45063668 |
| 11 | 362121760 |
| 12 | 2955642508 |
| 13 | 24284658100 |
| 14 | 201428123040 |
| 15 | 1680921310635 |
| 16 | 14119413718770 |
| 17 | 119205791509200 |
| 18 | 1011387051005100 |
| 19 | 8617021562542470 |
| 20 | 73704123363739440 |
| 21 | 632601537174078420 |
[1,1,8,35,266,1680,12804,93093,726440,5635058, 45063668,362121760,2955642508,24284658100, 201428123040,1680921310635,14119413718770, 119205791509200,1011387051005100,8617021562542470, 73704123363739440,632601537174078420] |