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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 9 |
| 7 | 25 |
| 8 | 75 |
| 9 | 195 |
| 10 | 475 |
| 11 | 1265 |
| 12 | 3135 |
| 13 | 7983 |
| 14 | 19697 |
| 15 | 50003 |
| 16 | 126163 |
| 17 | 317629 |
| 18 | 802945 |
| 19 | 2035619 |
| 20 | 5158039 |
| 21 | 13084381 |
| 22 | 33240845 |
| 23 | 84478199 |
| 24 | 214717585 |
| 25 | 546235003 |
| 26 | 1389896683 |
| 27 | 3537930077 |
| 28 | 9007910913 |
[0,0,0,1,4,9,25,75,195,475,1265,3135,7983,19697, 50003,126163,317629,802945,2035619,5158039, 13084381,33240845,84478199,214717585,546235003, 1389896683,3537930077,9007910913] |