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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 20 |
| 6 | 2910 |
| 7 | 22722 |
| 8 | 117656 |
| 9 | 8482392 |
| 10 | 143398170 |
| 11 | 1519998590 |
| 12 | 79655138772 |
| 13 | 2206506673956 |
| 14 | 39101112995126 |
| 15 | 1798446230741370 |
| 16 | 68667380639283120 |
| 17 | 1795441154500375472 |
| 18 | 81344029377887798706 |
| 19 | 3830461514154681289974 |
| 20 | 135388937631209203030700 |
[1,0,0,6,12,20,2910,22722,117656,8482392, 143398170,1519998590,79655138772,2206506673956, 39101112995126,1798446230741370,68667380639283120, 1795441154500375472,81344029377887798706, 3830461514154681289974,135388937631209203030700] |