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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 14 |
| 6 | 45 |
| 7 | 140 |
| 8 | 424 |
| 9 | 1269 |
| 10 | 3760 |
| 11 | 11080 |
| 12 | 32517 |
| 13 | 95190 |
| 14 | 278154 |
| 15 | 811887 |
| 16 | 2367973 |
| 17 | 6903453 |
| 18 | 20120905 |
| 19 | 58639016 |
| 20 | 170894228 |
| 21 | 498084608 |
| 22 | 1451899005 |
| 23 | 4232957241 |
| 24 | 12343454790 |
| 25 | 36001675800 |
| 26 | 105028397290 |
| 27 | 306472665459 |
| 28 | 894497511566 |
[0,0,1,4,14,45,140,424,1269,3760,11080,32517, 95190,278154,811887,2367973,6903453,20120905, 58639016,170894228,498084608,1451899005, 4232957241,12343454790,36001675800,105028397290, 306472665459,894497511566] |