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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 24 |
| 5 | 204 |
| 6 | 2635 |
| 7 | 39990 |
| 8 | 720916 |
| 9 | 14913192 |
| 10 | 348684381 |
| 11 | 9090909090 |
| 12 | 261535848376 |
| 13 | 8230246567620 |
| 14 | 281241174889207 |
| 15 | 10371206370593250 |
| 16 | 410525522392242720 |
| 17 | 17361641481138401520 |
| 18 | 781282469565908953017 |
| 19 | 37275544492386193492506 |
| 20 | 1879498672877604463254424 |
[1,1,2,24,204,2635,39990,720916,14913192, 348684381,9090909090,261535848376,8230246567620, 281241174889207,10371206370593250, 410525522392242720,17361641481138401520, 781282469565908953017,37275544492386193492506, 1879498672877604463254424] |