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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 330 |
| 6 | 2760 |
| 7 | 26670 |
| 8 | 295680 |
| 9 | 3686760 |
| 10 | 51067800 |
| 11 | 778239000 |
| 12 | 12937478400 |
| 13 | 232997965200 |
| 14 | 4518981066600 |
| 15 | 93905637625800 |
| 16 | 2081477759961600 |
| 17 | 49020847858382400 |
| 18 | 1222400311155223200 |
| 19 | 32175639432544608000 |
| 20 | 891491725439101987200 |
| 21 | 25935626681521134177600 |
| 22 | 790459388855441635730400 |
[1,1,2,9,48,330,2760,26670,295680,3686760, 51067800,778239000,12937478400,232997965200, 4518981066600,93905637625800,2081477759961600, 49020847858382400,1222400311155223200, 32175639432544608000,891491725439101987200, 25935626681521134177600,790459388855441635730400] |