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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 20 |
| 5 | 75 |
| 6 | 231 |
| 7 | 770 |
| 8 | 2988 |
| 9 | 11955 |
| 10 | 45925 |
| 11 | 171897 |
| 12 | 647855 |
| 13 | 2482753 |
| 14 | 9583140 |
| 15 | 36942528 |
| 16 | 142195548 |
| 17 | 548152335 |
| 18 | 2118999795 |
| 19 | 8207880490 |
| 20 | 31824803745 |
| 21 | 123488787719 |
| 22 | 479622307285 |
| 23 | 1864764751038 |
| 24 | 7256958446775 |
| 25 | 28263369668950 |
| 26 | 110152636824087 |
| 27 | 429590725414725 |
[1,0,0,3,20,75,231,770,2988,11955,45925,171897, 647855,2482753,9583140,36942528,142195548, 548152335,2118999795,8207880490,31824803745, 123488787719,479622307285,1864764751038, 7256958446775,28263369668950,110152636824087, 429590725414725] |