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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 6912 |
| 5 | 216000000 |
| 6 | 1632586752000000000 |
| 7 | 498266101635303733401600000000000 |
| 8 | 1140494258799407218656986754465090350453096448000000000000000 |
[1,1,2,18,6912,216000000,1632586752000000000, 498266101635303733401600000000000, 11404942587994072186569867544650903504530964480000\ 00000000000] |