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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 218 |
| 5 | 2475 |
| 6 | 34696 |
| 7 | 579223 |
| 8 | 11220540 |
| 9 | 247395097 |
| 10 | 6117023600 |
| 11 | 167639670441 |
| 12 | 5044046990776 |
| 13 | 165322086357715 |
| 14 | 5863394794421088 |
| 15 | 223751099288794375 |
| 16 | 9141963589243198736 |
| 17 | 398198217292835137137 |
| 18 | 18420080017512816009280 |
| 19 | 901874615547758970425977 |
[1,1,4,25,218,2475,34696,579223,11220540, 247395097,6117023600,167639670441,5044046990776, 165322086357715,5863394794421088, 223751099288794375,9141963589243198736, 398198217292835137137,18420080017512816009280, 901874615547758970425977] |