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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 2040 |
| 7 | 20160 |
| 8 | 231840 |
| 9 | 3024000 |
| 10 | 44271360 |
| 11 | 718502400 |
| 12 | 12813292800 |
| 13 | 249080832000 |
| 14 | 5243151513600 |
| 15 | 118824010905600 |
| 16 | 2884729655808000 |
| 17 | 74694359900160000 |
| 18 | 2054806272110592000 |
| 19 | 59849389401145344000 |
| 20 | 1840003788783992832000 |
| 21 | 59545276650123264000000 |
[0,0,2,6,36,240,2040,20160,231840,3024000, 44271360,718502400,12813292800,249080832000, 5243151513600,118824010905600,2884729655808000, 74694359900160000,2054806272110592000, 59849389401145344000,1840003788783992832000, 59545276650123264000000] |