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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 10 |
| 5 | 48 |
| 6 | 252 |
| 7 | 1584 |
| 8 | 10800 |
| 9 | 93600 |
| 10 | 823680 |
| 11 | 8588160 |
| 12 | 93381120 |
| 13 | 1158312960 |
| 14 | 14805504000 |
| 15 | 215028172800 |
| 16 | 3159494553600 |
| 17 | 51973589606400 |
| 18 | 873152856576000 |
| 19 | 16058241239040000 |
| 20 | 300754643245056000 |
| 21 | 6159522883497984000 |
| 22 | 127439374149255168000 |
[1,1,1,4,10,48,252,1584,10800,93600,823680, 8588160,93381120,1158312960,14805504000, 215028172800,3159494553600,51973589606400, 873152856576000,16058241239040000, 300754643245056000,6159522883497984000, 127439374149255168000] |