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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 55 |
| 4 | 198 |
| 5 | 706 |
| 6 | 2510 |
| 7 | 8923 |
| 8 | 31737 |
| 9 | 112918 |
| 10 | 401799 |
| 11 | 1429744 |
| 12 | 5087461 |
| 13 | 18102522 |
| 14 | 64413263 |
| 15 | 229198253 |
| 16 | 815544198 |
| 17 | 2901909494 |
| 18 | 10325718678 |
| 19 | 36741486569 |
| 20 | 130735386073 |
| 21 | 465189151460 |
| 22 | 1655259161187 |
| 23 | 5889825416864 |
| 24 | 20957469541173 |
| 25 | 74571909803996 |
[1,4,15,55,198,706,2510,8923,31737,112918,401799, 1429744,5087461,18102522,64413263,229198253, 815544198,2901909494,10325718678,36741486569, 130735386073,465189151460,1655259161187, 5889825416864,20957469541173,74571909803996] |