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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 40 |
| 3 | 160 |
| 4 | 5600 |
| 5 | 4480 |
| 6 | 44800 |
| 7 | 25600 |
| 8 | 4928000 |
| 9 | 3942400 |
| 10 | 73216000 |
| 11 | 186368000 |
| 12 | 501760000 |
| 13 | 2007040000 |
| 14 | 48742400000 |
| 15 | 38993920000 |
| 16 | 71310131200000 |
| 17 | 16778854400000 |
| 18 | 167788544000000 |
| 19 | 1412956160000 |
| 20 | 73932931072000000 |
| 21 | 42247389184000000 |
[1,4,40,160,5600,4480,44800,25600,4928000,3942400, 73216000,186368000,501760000,2007040000, 48742400000,38993920000,71310131200000, 16778854400000,167788544000000,1412956160000, 73932931072000000,42247389184000000] |