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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 7 |
| 3 | 24 |
| 4 | 108 |
| 5 | 600 |
| 6 | 3960 |
| 7 | 30240 |
| 8 | 262080 |
| 9 | 2540160 |
| 10 | 27216000 |
| 11 | 319334400 |
| 12 | 4071513600 |
| 13 | 56043187200 |
| 14 | 828193766400 |
| 15 | 13076743680000 |
| 16 | 219689293824000 |
| 17 | 3912561709056000 |
| 18 | 73627297615872000 |
| 19 | 1459741204905984000 |
| 20 | 30411275102208000000 |
| 21 | 664182248232222720000 |
[1,3,7,24,108,600,3960,30240,262080,2540160, 27216000,319334400,4071513600,56043187200, 828193766400,13076743680000,219689293824000, 3912561709056000,73627297615872000, 1459741204905984000,30411275102208000000, 664182248232222720000] |