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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 16 |
| 3 | 130 |
| 4 | 1120 |
| 5 | 9922 |
| 6 | 88816 |
| 7 | 797890 |
| 8 | 7176640 |
| 9 | 64576642 |
| 10 | 581150416 |
| 11 | 5230235650 |
| 12 | 47071766560 |
| 13 | 423644836162 |
| 14 | 3812800336816 |
| 15 | 34315193465410 |
| 16 | 308836712490880 |
| 17 | 2779530326324482 |
| 18 | 25015772678640016 |
| 19 | 225141953332919170 |
| 20 | 2026277577671749600 |
[0,2,16,130,1120,9922,88816,797890,7176640, 64576642,581150416,5230235650,47071766560, 423644836162,3812800336816,34315193465410, 308836712490880,2779530326324482, 25015772678640016,225141953332919170, 2026277577671749600] |