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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 10 |
| 3 | 72 |
| 4 | 670 |
| 5 | 7896 |
| 6 | 113532 |
| 7 | 1938948 |
| 8 | 38463150 |
| 9 | 869969602 |
| 10 | 22098936536 |
| 11 | 622728174288 |
| 12 | 19271479902324 |
| 13 | 649553475002720 |
| 14 | 23680210649058960 |
| 15 | 928276725059295192 |
| 16 | 38931910620358040382 |
| 17 | 1739307894106738293052 |
| 18 | 82457731356894087128054 |
| 19 | 4134332188240252347401752 |
| 20 | 218571692793801915329820184 |
[1,2,10,72,670,7896,113532,1938948,38463150, 869969602,22098936536,622728174288,19271479902324, 649553475002720,23680210649058960, 928276725059295192,38931910620358040382, 1739307894106738293052,82457731356894087128054, 4134332188240252347401752, 218571692793801915329820184] |