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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 4 |
| 5 | 10 |
| 6 | 20 |
| 7 | 35 |
| 8 | 1736 |
| 9 | 15204 |
| 10 | 88320 |
| 11 | 415965 |
| 12 | 7632460 |
| 13 | 121801966 |
| 14 | 1368227224 |
| 15 | 12184672955 |
| 16 | 176889193040 |
| 17 | 3490851044360 |
| 18 | 59703361471296 |
| 19 | 837948141904569 |
| 20 | 13407228541467540 |
| 21 | 283596013866706450 |
| 22 | 6226093732482731800 |
| 23 | 121326684752194084471 |
[1,0,0,0,4,10,20,35,1736,15204,88320,415965, 7632460,121801966,1368227224,12184672955, 176889193040,3490851044360,59703361471296, 837948141904569,13407228541467540, 283596013866706450,6226093732482731800, 121326684752194084471] |