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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 10 |
| 3 | 56 |
| 4 | 120 |
| 5 | 432 |
| 6 | 12672 |
| 7 | 249600 |
| 8 | 873180 |
| 9 | 4838400 |
| 10 | 296110080 |
| 11 | 10786406400 |
| 12 | 49621572000 |
| 13 | 355053404160 |
| 14 | 34613526528000 |
| 15 | 211189410432000 |
| 16 | 1910897049600000 |
| 17 | 21311651380219200 |
| 18 | 274774815041126400 |
| 19 | 62908970812047360000 |
[3,10,56,120,432,12672,249600,873180,4838400, 296110080,10786406400,49621572000,355053404160, 34613526528000,211189410432000,1910897049600000, 21311651380219200,274774815041126400, 62908970812047360000] |