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| n | a(n) |
|---|---|
| 3 | 1 |
| 4 | 4 |
| 5 | 15 |
| 6 | 50 |
| 7 | 161 |
| 8 | 504 |
| 9 | 1553 |
| 10 | 4730 |
| 11 | 14289 |
| 12 | 42900 |
| 13 | 128193 |
| 14 | 381654 |
| 15 | 1132950 |
| 16 | 3355392 |
| 17 | 9918990 |
| 18 | 29278012 |
| 19 | 86316259 |
| 20 | 254227980 |
| 21 | 748200145 |
| 22 | 2200619806 |
| 23 | 6469372932 |
| 24 | 19011518480 |
| 25 | 55853259800 |
| 26 | 164055406320 |
| 27 | 481804384035 |
| 28 | 1414857108756 |
| 29 | 4154663090529 |
[1,4,15,50,161,504,1553,4730,14289,42900,128193, 381654,1132950,3355392,9918990,29278012,86316259, 254227980,748200145,2200619806,6469372932, 19011518480,55853259800,164055406320,481804384035, 1414857108756,4154663090529] |