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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 126 |
| 3 | 63 |
| 4 | 2646 |
| 5 | 7938 |
| 6 | 611226 |
| 7 | 1047816 |
| 8 | 6501222 |
| 9 | 47675628 |
| 10 | 250297047 |
| 11 | 546102648 |
| 12 | 89356045779 |
| 13 | 5891607414 |
| 14 | 9403005432744 |
| 15 | 18806010865488 |
| 16 | 58341374616798 |
| 17 | 56625451833951 |
| 18 | 133711566930569628 |
| 19 | 21112352673247836 |
| 20 | 221679703069102278 |
[1,6,126,63,2646,7938,611226,1047816,6501222, 47675628,250297047,546102648,89356045779, 5891607414,9403005432744,18806010865488, 58341374616798,56625451833951,133711566930569628, 21112352673247836,221679703069102278] |