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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 140 |
| 5 | 1134 |
| 6 | 9702 |
| 7 | 87516 |
| 8 | 817245 |
| 9 | 7852130 |
| 10 | 77135630 |
| 11 | 771742608 |
| 12 | 7839348244 |
| 13 | 80661853300 |
| 14 | 839138980500 |
| 15 | 8813312133840 |
| 16 | 93339369441540 |
| 17 | 995827949882370 |
| 18 | 10694044148599350 |
| 19 | 115515073043785800 |
| 20 | 1254354063204682440 |
| 21 | 13685749828961247180 |
[1,1,3,20,140,1134,9702,87516,817245,7852130, 77135630,771742608,7839348244,80661853300, 839138980500,8813312133840,93339369441540, 995827949882370,10694044148599350, 115515073043785800,1254354063204682440, 13685749828961247180] |