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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 3 |
| 3 | 12 |
| 4 | 90 |
| 5 | 660 |
| 6 | 5565 |
| 7 | 51912 |
| 8 | 533988 |
| 9 | 6007320 |
| 10 | 73422855 |
| 11 | 969181620 |
| 12 | 13744757598 |
| 13 | 208462156812 |
| 14 | 3367465610145 |
| 15 | 57727981888080 |
| 16 | 1046800738237320 |
| 17 | 20020064118788592 |
| 18 | 402756584036805963 |
| 19 | 8502638996332570140 |
| 20 | 187953072550509445410 |
| 21 | 4341715975916768188740 |
[0,0,3,12,90,660,5565,51912,533988,6007320, 73422855,969181620,13744757598,208462156812, 3367465610145,57727981888080,1046800738237320, 20020064118788592,402756584036805963, 8502638996332570140,187953072550509445410, 4341715975916768188740] |