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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 28 |
| 3 | 660 |
| 4 | 20020 |
| 5 | 705432 |
| 6 | 27457584 |
| 7 | 1147334760 |
| 8 | 50561468100 |
| 9 | 2322279359400 |
| 10 | 110250966574320 |
| 11 | 5377893986141040 |
| 12 | 268315541493159888 |
| 13 | 13645106597301720800 |
| 14 | 705378072079232798400 |
| 15 | 36985702814877062972880 |
| 16 | 1963555139681260758978660 |
| 17 | 105393959626252993455319560 |
[1,2,28,660,20020,705432,27457584,1147334760, 50561468100,2322279359400,110250966574320, 5377893986141040,268315541493159888, 13645106597301720800,705378072079232798400, 36985702814877062972880,1963555139681260758978660, 105393959626252993455319560] |