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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 14 |
| 4 | 48 |
| 5 | 424 |
| 6 | 3360 |
| 7 | 30288 |
| 8 | 276864 |
| 9 | 3591936 |
| 10 | 46241280 |
| 11 | 599212800 |
| 12 | 9205954560 |
| 13 | 142744412160 |
| 14 | 2554915184640 |
| 15 | 47649718609920 |
| 16 | 907617573273600 |
| 17 | 18296536869273600 |
| 18 | 413470794456760320 |
| 19 | 9130651338347642880 |
| 20 | 221996730181563187200 |
[1,1,2,14,48,424,3360,30288,276864,3591936, 46241280,599212800,9205954560,142744412160, 2554915184640,47649718609920,907617573273600, 18296536869273600,413470794456760320, 9130651338347642880,221996730181563187200] |