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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 4950 |
| 8 | 38880 |
| 9 | 343440 |
| 10 | 3369600 |
| 11 | 36352800 |
| 12 | 427680000 |
| 13 | 5452027218 |
| 14 | 74846801304 |
| 15 | 1100895311340 |
| 16 | 17272089457920 |
| 17 | 287920937620800 |
| 18 | 5081935953473280 |
| 19 | 94681381716805374 |
| 20 | 1856848184953043760 |
| 21 | 38236452673395920040 |
| 22 | 824863858830361247040 |
[1,1,2,6,24,120,720,4950,38880,343440,3369600, 36352800,427680000,5452027218,74846801304, 1100895311340,17272089457920,287920937620800, 5081935953473280,94681381716805374, 1856848184953043760,38236452673395920040, 824863858830361247040] |