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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 20 |
| 6 | 750 |
| 7 | 7602 |
| 8 | 47096 |
| 9 | 589752 |
| 10 | 11823930 |
| 11 | 169812830 |
| 12 | 2287327812 |
| 13 | 46793930196 |
| 14 | 1061518458182 |
| 15 | 21163158296490 |
| 16 | 458344052450160 |
| 17 | 12165772611938672 |
| 18 | 329982890581149426 |
| 19 | 8764089834124752822 |
| 20 | 255655700917556204540 |
| 21 | 8220667673623130347020 |
[1,0,0,6,12,20,750,7602,47096,589752,11823930, 169812830,2287327812,46793930196,1061518458182, 21163158296490,458344052450160,12165772611938672, 329982890581149426,8764089834124752822, 255655700917556204540,8220667673623130347020] |