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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 28 |
| 6 | 200 |
| 7 | 2196 |
| 8 | 37004 |
| 9 | 957304 |
| 10 | 38016960 |
| 11 | 2317631400 |
| 12 | 216893681800 |
| 13 | 31159166587056 |
| 14 | 6871649018572800 |
| 15 | 2326335506123418128 |
| 16 | 1208982377794384163088 |
| 17 | 964503557426086478029152 |
| 18 | 1181201363574177619007442944 |
| 19 | 2220650888749669503773432361504 |
| 20 | 6408743336016148761893699822360672 |
[1,1,1,2,6,28,200,2196,37004,957304,38016960, 2317631400,216893681800,31159166587056, 6871649018572800,2326335506123418128, 1208982377794384163088,964503557426086478029152, 1181201363574177619007442944, 2220650888749669503773432361504, 6408743336016148761893699822360672] |