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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 120 |
| 5 | 1320 |
| 6 | 15120 |
| 7 | 216720 |
| 8 | 3427200 |
| 9 | 62052480 |
| 10 | 1237420800 |
| 11 | 27263174400 |
| 12 | 653837184000 |
| 13 | 17005993804800 |
| 14 | 476080648243200 |
| 15 | 14283727121664000 |
| 16 | 457058345103360000 |
| 17 | 15540339420942336000 |
[1,1,2,18,120,1320,15120,216720,3427200,62052480, 1237420800,27263174400,653837184000, 17005993804800,476080648243200,14283727121664000, 457058345103360000,15540339420942336000] |