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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 21 |
| 4 | 210 |
| 5 | 2574 |
| 6 | 36036 |
| 7 | 554268 |
| 8 | 9145422 |
| 9 | 159352050 |
| 10 | 2900207310 |
| 11 | 54698315490 |
| 12 | 1062710129520 |
| 13 | 21172455657360 |
| 14 | 431010704453400 |
| 15 | 8939669081780520 |
| 16 | 188478023140872630 |
| 17 | 4031562420682009290 |
| 18 | 87350519114776867950 |
| 19 | 1914486941500560677250 |
| 20 | 42397183540866961907100 |
[1,3,21,210,2574,36036,554268,9145422,159352050, 2900207310,54698315490,1062710129520, 21172455657360,431010704453400,8939669081780520, 188478023140872630,4031562420682009290, 87350519114776867950,1914486941500560677250, 42397183540866961907100] |