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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 32 |
| 3 | 288 |
| 4 | 2560 |
| 5 | 26400 |
| 6 | 165888 |
| 7 | 2384928 |
| 8 | 15728640 |
| 9 | 141087744 |
| 10 | 1246080000 |
| 11 | 14758128000 |
| 12 | 85996339200 |
| 13 | 1270928131200 |
| 14 | 8810420097024 |
| 15 | 70207948800000 |
| 16 | 677066362060800 |
| 17 | 8218041445152000 |
| 18 | 43129128265187328 |
| 19 | 674757689572915200 |
| 20 | 4238841176064000000 |
[4,32,288,2560,26400,165888,2384928,15728640, 141087744,1246080000,14758128000,85996339200, 1270928131200,8810420097024,70207948800000, 677066362060800,8218041445152000, 43129128265187328,674757689572915200, 4238841176064000000] |