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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 10 |
| 4 | 20 |
| 5 | 237 |
| 6 | 770 |
| 7 | 3944 |
| 8 | 28635 |
| 9 | 112360 |
| 10 | 744084 |
| 11 | 4381083 |
| 12 | 21579779 |
| 13 | 143815322 |
| 14 | 801165187 |
| 15 | 4578481584 |
| 16 | 29176623983 |
| 17 | 165772480380 |
| 18 | 1013147794546 |
| 19 | 6259309820475 |
| 20 | 36974951346176 |
| 21 | 230752749518819 |
| 22 | 1413352914731005 |
| 23 | 8618746801792237 |
| 24 | 53986291171211635 |
[1,0,3,10,20,237,770,3944,28635,112360,744084, 4381083,21579779,143815322,801165187,4578481584, 29176623983,165772480380,1013147794546, 6259309820475,36974951346176,230752749518819, 1413352914731005,8618746801792237, 53986291171211635] |