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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 48 |
| 3 | 336 |
| 4 | 2394 |
| 5 | 16752 |
| 6 | 117600 |
| 7 | 823152 |
| 8 | 5764416 |
| 9 | 40350870 |
| 10 | 282472512 |
| 11 | 1977307248 |
| 12 | 13841268048 |
| 13 | 96888873648 |
| 14 | 678222936384 |
| 15 | 4747560552384 |
| 16 | 33232929612330 |
| 17 | 232630507267536 |
| 18 | 1628413591207536 |
| 19 | 11398895138319024 |
| 20 | 79792266250574640 |
| 21 | 558545863753891104 |
[1,6,48,336,2394,16752,117600,823152,5764416, 40350870,282472512,1977307248,13841268048, 96888873648,678222936384,4747560552384, 33232929612330,232630507267536,1628413591207536, 11398895138319024,79792266250574640, 558545863753891104] |