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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 21 |
| 5 | 181 |
| 6 | 1815 |
| 7 | 20154 |
| 8 | 241665 |
| 9 | 3080331 |
| 10 | 41302128 |
| 11 | 578300961 |
| 12 | 8410381731 |
| 13 | 126533164302 |
| 14 | 1963198249559 |
| 15 | 31334634890994 |
| 16 | 513482316151767 |
| 17 | 8625106767201627 |
| 18 | 148306563373055094 |
| 19 | 2607509241485053311 |
| 20 | 46832500213908831048 |
| 21 | 858557964325898228058 |
[1,1,3,21,181,1815,20154,241665,3080331,41302128, 578300961,8410381731,126533164302,1963198249559, 31334634890994,513482316151767,8625106767201627, 148306563373055094,2607509241485053311, 46832500213908831048,858557964325898228058] |