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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 176 |
| 6 | 1540 |
| 7 | 15672 |
| 8 | 181916 |
| 9 | 2372512 |
| 10 | 34348932 |
| 11 | 546674120 |
| 12 | 9486840748 |
| 13 | 178285201008 |
| 14 | 3607174453844 |
| 15 | 78177409231768 |
| 16 | 1806934004612220 |
| 17 | 44367502983673664 |
| 18 | 1153334584544496676 |
| 19 | 31643148872573831016 |
[0,0,1,4,24,176,1540,15672,181916,2372512, 34348932,546674120,9486840748,178285201008, 3607174453844,78177409231768,1806934004612220, 44367502983673664,1153334584544496676, 31643148872573831016] |