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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 376 |
| 5 | 2220 |
| 6 | 125028 |
| 7 | 1614480 |
| 8 | 92285856 |
| 9 | 2018520000 |
| 10 | 121850616240 |
| 11 | 3907998135360 |
| 12 | 253836993367296 |
| 13 | 10891474747433280 |
| 14 | 768302761361304960 |
| 15 | 41447634607068318720 |
| 16 | 3187906294983450762240 |
| 17 | 206982374312337802536960 |
| 18 | 17368877655215923728595968 |
[1,0,4,6,376,2220,125028,1614480,92285856, 2018520000,121850616240,3907998135360, 253836993367296,10891474747433280, 768302761361304960,41447634607068318720, 3187906294983450762240,206982374312337802536960, 17368877655215923728595968] |