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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 50 |
| 3 | 840 |
| 4 | 16215 |
| 5 | 339416 |
| 6 | 7492342 |
| 7 | 171714400 |
| 8 | 4046995095 |
| 9 | 97464474800 |
| 10 | 2388021782916 |
| 11 | 59337354111464 |
| 12 | 1491714713034000 |
| 13 | 37872300445759440 |
| 14 | 969656048236053850 |
| 15 | 25008097347083474496 |
| 16 | 649098691321081570855 |
| 17 | 16942574600154870074100 |
[1,4,50,840,16215,339416,7492342,171714400, 4046995095,97464474800,2388021782916, 59337354111464,1491714713034000,37872300445759440, 969656048236053850,25008097347083474496, 649098691321081570855,16942574600154870074100] |