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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 0 |
| 5 | 0 |
| 6 | 160 |
| 7 | 544 |
| 8 | 0 |
| 9 | 17920 |
| 10 | 261120 |
| 11 | 707584 |
| 12 | 3942400 |
| 13 | 149360640 |
| 14 | 1538068480 |
| 15 | 5242548224 |
| 16 | 111522611200 |
| 17 | 2782416732160 |
| 18 | 25458261360640 |
| 19 | 166243180478464 |
| 20 | 5279051703910400 |
| 21 | 109528131284500480 |
[1,0,0,4,0,0,160,544,0,17920,261120,707584, 3942400,149360640,1538068480,5242548224, 111522611200,2782416732160,25458261360640, 166243180478464,5279051703910400, 109528131284500480] |