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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 8 |
| 6 | 39 |
| 7 | 189 |
| 8 | 907 |
| 9 | 4348 |
| 10 | 21099 |
| 11 | 103676 |
| 12 | 516314 |
| 13 | 2602561 |
| 14 | 13265172 |
| 15 | 68282899 |
| 16 | 354610139 |
| 17 | 1856180378 |
| 18 | 9785234438 |
| 19 | 51915995526 |
| 20 | 277044420920 |
[0,0,0,1,8,39,189,907,4348,21099,103676,516314, 2602561,13265172,68282899,354610139,1856180378, 9785234438,51915995526,277044420920] |