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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 16 |
| 5 | 96 |
| 6 | 576 |
| 7 | 4320 |
| 8 | 31872 |
| 9 | 298368 |
| 10 | 3052800 |
| 11 | 34387200 |
| 12 | 404029440 |
| 13 | 5339473920 |
| 14 | 75893207040 |
| 15 | 1139356108800 |
| 16 | 18079668633600 |
| 17 | 310896849715200 |
| 18 | 5654417758617600 |
| 19 | 107707364764876800 |
| 20 | 2145784566959308800 |
| 21 | 45252164164799692800 |
| 22 | 1003024255355781120000 |
[0,0,2,4,16,96,576,4320,31872,298368,3052800, 34387200,404029440,5339473920,75893207040, 1139356108800,18079668633600,310896849715200, 5654417758617600,107707364764876800, 2145784566959308800,45252164164799692800, 1003024255355781120000] |