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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 56 |
| 5 | 536 |
| 6 | 6336 |
| 7 | 89984 |
| 8 | 1502080 |
| 9 | 28816000 |
| 10 | 624183040 |
| 11 | 15068741632 |
| 12 | 401279717376 |
| 13 | 11686228873216 |
| 14 | 369481496674304 |
| 15 | 12604143513731072 |
| 16 | 461450753988067328 |
| 17 | 18047560103055097856 |
| 18 | 750979001470906073088 |
| 19 | 33127742823550018125824 |
| 20 | 1544257684260700601712640 |
[1,1,2,8,56,536,6336,89984,1502080,28816000, 624183040,15068741632,401279717376,11686228873216, 369481496674304,12604143513731072, 461450753988067328,18047560103055097856, 750979001470906073088,33127742823550018125824, 1544257684260700601712640] |