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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 719 |
| 7 | 5027 |
| 8 | 40168 |
| 9 | 361080 |
| 10 | 3606480 |
| 11 | 39623760 |
| 12 | 474915803 |
| 13 | 6166512899 |
| 14 | 86227808578 |
| 15 | 1291868401830 |
| 16 | 20645144452320 |
| 17 | 350547210173280 |
| 18 | 6302294420371031 |
| 19 | 119600213982762899 |
| 20 | 2389140113204434900 |
| 21 | 50111866901959213980 |
| 22 | 1101140993932295832120 |
[1,1,2,6,24,120,719,5027,40168,361080,3606480, 39623760,474915803,6166512899,86227808578, 1291868401830,20645144452320,350547210173280, 6302294420371031,119600213982762899, 2389140113204434900,50111866901959213980, 1101140993932295832120] |