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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 640 |
| 5 | 34720 |
| 6 | 533760 |
| 7 | 4735360 |
| 8 | 30822400 |
| 9 | 164183040 |
| 10 | 759521280 |
| 11 | 3163607040 |
| 12 | 12148899840 |
| 13 | 43724595200 |
| 14 | 149243494400 |
| 15 | 487404503040 |
| 16 | 1533406085120 |
| 17 | 4672095518720 |
| 18 | 13845292646400 |
| 19 | 40043324375040 |
| 20 | 113352785264640 |
| 21 | 314803035832320 |
| 22 | 859445521285120 |
[0,0,0,640,34720,533760,4735360,30822400, 164183040,759521280,3163607040,12148899840, 43724595200,149243494400,487404503040, 1533406085120,4672095518720,13845292646400, 40043324375040,113352785264640,314803035832320, 859445521285120] |