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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 40 |
| 5 | 372 |
| 6 | 3815 |
| 7 | 41652 |
| 8 | 474980 |
| 9 | 5591912 |
| 10 | 67454545 |
| 11 | 829438722 |
| 12 | 10358083621 |
| 13 | 131013535954 |
| 14 | 1674940506728 |
| 15 | 21608978465341 |
| 16 | 280976960703472 |
| 17 | 3678460005228692 |
| 18 | 48446069275681169 |
| 19 | 641429612434785006 |
| 20 | 8532711384899213885 |
| 21 | 113988520118626013998 |
[1,0,1,5,40,372,3815,41652,474980,5591912, 67454545,829438722,10358083621,131013535954, 1674940506728,21608978465341,280976960703472, 3678460005228692,48446069275681169, 641429612434785006,8532711384899213885, 113988520118626013998] |