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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 255 |
| 4 | 624 |
| 5 | 14640 |
| 6 | 65280 |
| 7 | 707280 |
| 8 | 4100000 |
| 9 | 33361920 |
| 10 | 214344240 |
| 11 | 1568239200 |
| 12 | 10485693840 |
| 13 | 73680216480 |
| 14 | 500245705680 |
| 15 | 3461445351120 |
| 16 | 23639283000000 |
| 17 | 162614549665680 |
| 18 | 1113034754027520 |
| 19 | 7639424429247600 |
| 20 | 52333710967281120 |
| 21 | 358890347608872240 |
[1,0,255,624,14640,65280,707280,4100000,33361920, 214344240,1568239200,10485693840,73680216480, 500245705680,3461445351120,23639283000000, 162614549665680,1113034754027520,7639424429247600, 52333710967281120,358890347608872240] |