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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 56 |
| 4 | 1112 |
| 5 | 25000 |
| 6 | 607712 |
| 7 | 15918280 |
| 8 | 451371888 |
| 9 | 13908978792 |
| 10 | 466254401360 |
| 11 | 16972978214456 |
| 12 | 668532916285104 |
| 13 | 28362769354991656 |
| 14 | 1290007395847848160 |
| 15 | 62619708755213093360 |
| 16 | 3230982278203826268640 |
| 17 | 176553522584025285715304 |
| 18 | 10184062836771923067636528 |
[1,4,56,1112,25000,607712,15918280,451371888, 13908978792,466254401360,16972978214456, 668532916285104,28362769354991656, 1290007395847848160,62619708755213093360, 3230982278203826268640,176553522584025285715304, 10184062836771923067636528] |