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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 90 |
| 4 | 723 |
| 5 | 10689 |
| 6 | 130428 |
| 7 | 1862580 |
| 8 | 25594611 |
| 9 | 368313993 |
| 10 | 5289203262 |
| 11 | 77279744418 |
| 12 | 1134460916361 |
| 13 | 16798605635235 |
| 14 | 249994099311288 |
| 15 | 3740771822960664 |
| 16 | 56208829313956998 |
| 17 | 847934859174601650 |
| 18 | 12834366187138678836 |
| 19 | 194855374723972622988 |
| 20 | 2966358133685609559042 |
[1,3,6,90,723,10689,130428,1862580,25594611, 368313993,5289203262,77279744418,1134460916361, 16798605635235,249994099311288,3740771822960664, 56208829313956998,847934859174601650, 12834366187138678836,194855374723972622988, 2966358133685609559042] |