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| n | a(n) |
|---|---|
| 2 | 18 |
| 3 | 1080 |
| 4 | 99248 |
| 5 | 6710160 |
| 6 | 312975306 |
| 7 | 8820400232 |
| 8 | 155825544448 |
| 9 | 1902742912440 |
| 10 | 17422385919290 |
| 11 | 126966804496576 |
| 12 | 769002076834992 |
| 13 | 3997219502682952 |
| 14 | 18271131867527266 |
| 15 | 74845992604425840 |
| 16 | 278918348891883520 |
| 17 | 957055146953124368 |
| 18 | 3053791953265318722 |
[18,1080,99248,6710160,312975306,8820400232, 155825544448,1902742912440,17422385919290, 126966804496576,769002076834992,3997219502682952, 18271131867527266,74845992604425840, 278918348891883520,957055146953124368, 3053791953265318722] |