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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 30 |
| 4 | 24 |
| 5 | 1210 |
| 6 | 18396 |
| 7 | 235998 |
| 8 | 4793456 |
| 9 | 76168850 |
| 10 | 1282320348 |
| 11 | 25100418046 |
| 12 | 481341997032 |
| 13 | 10452086347274 |
| 14 | 237925595533164 |
| 15 | 5524220670435982 |
| 16 | 136705837928870368 |
| 17 | 3444192369181374754 |
| 18 | 89772662325079950436 |
| 19 | 2431910317560215089758 |
| 20 | 67517711482300160612104 |
[1,2,4,30,24,1210,18396,235998,4793456,76168850, 1282320348,25100418046,481341997032, 10452086347274,237925595533164,5524220670435982, 136705837928870368,3444192369181374754, 89772662325079950436,2431910317560215089758, 67517711482300160612104] |