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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 55 |
| 3 | 3080 |
| 4 | 176855 |
| 5 | 10343256 |
| 6 | 613052440 |
| 7 | 36701926976 |
| 8 | 2214353424855 |
| 9 | 134425330290680 |
| 10 | 8201448540559560 |
| 11 | 502460159228920256 |
| 12 | 30890758976011469080 |
| 13 | 1904794982716556862400 |
| 14 | 117756015163729064222400 |
| 15 | 7296082202981986626900480 |
| 16 | 452950299939910627966962135 |
[0,1,55,3080,176855,10343256,613052440, 36701926976,2214353424855,134425330290680, 8201448540559560,502460159228920256, 30890758976011469080,1904794982716556862400, 117756015163729064222400, 7296082202981986626900480, 452950299939910627966962135] |