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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 20 |
| 6 | 315 |
| 7 | 4620 |
| 8 | 67830 |
| 9 | 1020600 |
| 10 | 15961050 |
| 11 | 260706600 |
| 12 | 4461170175 |
| 13 | 80002622700 |
| 14 | 1503527550525 |
| 15 | 29583578524500 |
| 16 | 608837350621500 |
| 17 | 13088359506222000 |
| 18 | 293538127312930500 |
| 19 | 6858722586405690000 |
| 20 | 166752692881988338125 |
[1,20,315,4620,67830,1020600,15961050,260706600, 4461170175,80002622700,1503527550525, 29583578524500,608837350621500,13088359506222000, 293538127312930500,6858722586405690000, 166752692881988338125] |