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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 25 |
| 6 | 90 |
| 7 | 301 |
| 8 | 966 |
| 9 | 3025 |
| 10 | 9330 |
| 11 | 28501 |
| 12 | 86526 |
| 13 | 261625 |
| 14 | 788970 |
| 15 | 2375101 |
| 16 | 7141686 |
| 17 | 21457825 |
| 18 | 64439010 |
| 19 | 193448101 |
| 20 | 580606446 |
| 21 | 1742343625 |
| 22 | 5228079450 |
| 23 | 15686335501 |
| 24 | 47063200806 |
| 25 | 141197991025 |
| 26 | 423610750290 |
| 27 | 1270865805301 |
[0,0,0,1,6,25,90,301,966,3025,9330,28501,86526, 261625,788970,2375101,7141686,21457825,64439010, 193448101,580606446,1742343625,5228079450, 15686335501,47063200806,141197991025,423610750290, 1270865805301] |