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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 46 |
| 4 | 456 |
| 5 | 5656 |
| 6 | 84336 |
| 7 | 1467376 |
| 8 | 29175936 |
| 9 | 652606336 |
| 10 | 16219458816 |
| 11 | 443419545856 |
| 12 | 13224580002816 |
| 13 | 427278468668416 |
| 14 | 14867050125981696 |
| 15 | 554245056343668736 |
| 16 | 22039796215883268096 |
| 17 | 931198483176870608896 |
| 18 | 41658202699736550014976 |
| 19 | 1967160945260218035798016 |
[1,1,6,46,456,5656,84336,1467376,29175936, 652606336,16219458816,443419545856,13224580002816, 427278468668416,14867050125981696, 554245056343668736,22039796215883268096, 931198483176870608896,41658202699736550014976, 1967160945260218035798016] |