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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 3 |
| 5 | 12 |
| 6 | 30 |
| 7 | 240 |
| 8 | 1050 |
| 9 | 16800 |
| 10 | 132300 |
| 11 | 4233600 |
| 12 | 61122600 |
| 13 | 3911846400 |
| 14 | 104886381600 |
| 15 | 13425456844800 |
| 16 | 674943865596000 |
| 17 | 172785629592576000 |
| 18 | 16407885372638760000 |
| 19 | 8400837310791045120000 |
| 20 | 1515727634953623371280000 |
| 21 | 1552105098192510332190720000 |
[1,1,1,2,3,12,30,240,1050,16800,132300,4233600, 61122600,3911846400,104886381600,13425456844800, 674943865596000,172785629592576000, 16407885372638760000,8400837310791045120000, 1515727634953623371280000, 1552105098192510332190720000] |