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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 255 |
| 3 | 3640 |
| 4 | 27525 |
| 5 | 154056 |
| 6 | 713850 |
| 7 | 2878920 |
| 8 | 10432650 |
| 9 | 34739200 |
| 10 | 107930865 |
| 11 | 316293000 |
| 12 | 881570320 |
| 13 | 2352362160 |
| 14 | 6040988775 |
| 15 | 14993606776 |
| 16 | 36092638500 |
| 17 | 84513447480 |
| 18 | 192980579410 |
| 19 | 430636071000 |
| 20 | 940847483976 |
| 21 | 2015771306800 |
| 22 | 4241235245220 |
| 23 | 8774382020520 |
[1,0,255,3640,27525,154056,713850,2878920, 10432650,34739200,107930865,316293000,881570320, 2352362160,6040988775,14993606776,36092638500, 84513447480,192980579410,430636071000, 940847483976,2015771306800,4241235245220, 8774382020520] |