| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 42 |
| 4 | 420 |
| 5 | 3720 |
| 6 | 31248 |
| 7 | 256032 |
| 8 | 2072640 |
| 9 | 16679040 |
| 10 | 133824768 |
| 11 | 1072169472 |
| 12 | 8583644160 |
| 13 | 68694312960 |
| 14 | 549655154688 |
| 15 | 4397643866112 |
| 16 | 35182761492480 |
| 17 | 281468534292480 |
| 18 | 2251774043947008 |
| 19 | 18014295430397952 |
| 20 | 144114775759257600 |
[0,3,42,420,3720,31248,256032,2072640,16679040, 133824768,1072169472,8583644160,68694312960, 549655154688,4397643866112,35182761492480, 281468534292480,2251774043947008, 18014295430397952,144114775759257600] |