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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 420 |
| 3 | 9296 |
| 4 | 216868 |
| 5 | 5313360 |
| 6 | 135866640 |
| 7 | 3599688000 |
| 8 | 98122746660 |
| 9 | 2735243498960 |
| 10 | 77595234251920 |
| 11 | 2231860533960000 |
| 12 | 64904359322352400 |
| 13 | 1904342118510144320 |
| 14 | 56285527873777258560 |
| 15 | 1673824975976543421696 |
| 16 | 50036226313229526706980 |
| 17 | 1502471400349641645458640 |
[1,20,420,9296,216868,5313360,135866640, 3599688000,98122746660,2735243498960, 77595234251920,2231860533960000,64904359322352400, 1904342118510144320,56285527873777258560, 1673824975976543421696,50036226313229526706980, 1502471400349641645458640] |