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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 90 |
| 2 | 656100 |
| 3 | 387420489000 |
| 4 | 18530201888518410000 |
| 5 | 71789798769185258877024900000 |
| 6 | 22528399544939174411840147874772641000000 |
[1,90,656100,387420489000,18530201888518410000, 71789798769185258877024900000, 22528399544939174411840147874772641000000] |