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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 12 |
| 5 | 60 |
| 6 | 300 |
| 7 | 1296 |
| 8 | 5616 |
| 9 | 28080 |
| 10 | 155520 |
| 11 | 883872 |
| 12 | 5018112 |
| 13 | 28304640 |
| 14 | 158130514 |
| 15 | 878719104 |
| 16 | 4899999744 |
| 17 | 27554100480 |
| 18 | 156139902720 |
| 19 | 889181991936 |
| 20 | 5077739844402 |
| 21 | 29043991855542 |
| 22 | 166348496793600 |
| 23 | 954240788994048 |
| 24 | 5484206701412352 |
| 25 | 31581437286776820 |
[0,0,2,12,60,300,1296,5616,28080,155520,883872, 5018112,28304640,158130514,878719104,4899999744, 27554100480,156139902720,889181991936, 5077739844402,29043991855542,166348496793600, 954240788994048,5484206701412352, 31581437286776820] |