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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 55 |
| 5 | 184 |
| 6 | 879 |
| 7 | 3283 |
| 8 | 15929 |
| 9 | 62222 |
| 10 | 305006 |
| 11 | 1233715 |
| 12 | 6081876 |
| 13 | 25181122 |
| 14 | 124578183 |
| 15 | 524939078 |
| 16 | 2603359344 |
| 17 | 11120535185 |
| 18 | 55244397220 |
| 19 | 238564600702 |
| 20 | 1186615992619 |
| 21 | 5170229157814 |
| 22 | 25740573127296 |
| 23 | 112994182925001 |
| 24 | 562957176960359 |
| 25 | 2486929397436891 |
| 26 | 12397280542469366 |
| 27 | 55065536289042493 |
[1,1,4,12,55,184,879,3283,15929,62222,305006, 1233715,6081876,25181122,124578183,524939078, 2603359344,11120535185,55244397220,238564600702, 1186615992619,5170229157814,25740573127296, 112994182925001,562957176960359,2486929397436891, 12397280542469366,55065536289042493] |