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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 210 |
| 6 | 2310 |
| 7 | 34650 |
| 8 | 762300 |
| 9 | 22869000 |
| 10 | 960498000 |
| 11 | 53787888000 |
| 12 | 4141667376000 |
| 13 | 418308404976000 |
| 14 | 56471634671760000 |
| 15 | 9939007702229760000 |
| 16 | 2295910779215074560000 |
| 17 | 681885501426877144320000 |
| 18 | 262525918049347700563200000 |
| 19 | 128637699844180373275968000000 |
[1,1,2,6,30,210,2310,34650,762300,22869000, 960498000,53787888000,4141667376000, 418308404976000,56471634671760000, 9939007702229760000,2295910779215074560000, 681885501426877144320000, 262525918049347700563200000, 128637699844180373275968000000] |