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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 80 |
| 5 | 325 |
| 6 | 1371 |
| 7 | 5945 |
| 8 | 26322 |
| 9 | 118456 |
| 10 | 539795 |
| 11 | 2485364 |
| 12 | 11541204 |
| 13 | 53971667 |
| 14 | 253912435 |
| 15 | 1200681742 |
| 16 | 5702732119 |
| 17 | 27189790932 |
| 18 | 130074587375 |
| 19 | 624117990312 |
| 20 | 3002521483738 |
| 21 | 14478663206101 |
| 22 | 69965966828818 |
| 23 | 338743936413194 |
| 24 | 1642874254072415 |
| 25 | 7980241381187844 |
| 26 | 38819241417135171 |
| 27 | 189079627020638500 |
[1,2,6,21,80,325,1371,5945,26322,118456,539795, 2485364,11541204,53971667,253912435,1200681742, 5702732119,27189790932,130074587375,624117990312, 3002521483738,14478663206101,69965966828818, 338743936413194,1642874254072415,7980241381187844, 38819241417135171,189079627020638500] |