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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 0 |
| 4 | 26 |
| 5 | 120 |
| 6 | 1922 |
| 7 | 21840 |
| 8 | 307946 |
| 9 | 4251240 |
| 10 | 63165842 |
| 11 | 1010729280 |
| 12 | 18501318266 |
| 13 | 391496665560 |
| 14 | 9265945721762 |
| 15 | 232411950454320 |
| 16 | 5972325812958986 |
| 17 | 156131611764907080 |
| 18 | 4208451299935189682 |
| 19 | 119669466221148348960 |
| 20 | 3658459009408581118106 |
[1,0,2,0,26,120,1922,21840,307946,4251240, 63165842,1010729280,18501318266,391496665560, 9265945721762,232411950454320,5972325812958986, 156131611764907080,4208451299935189682, 119669466221148348960,3658459009408581118106] |