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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 56 |
| 3 | 1320 |
| 4 | 43680 |
| 5 | 1860480 |
| 6 | 96909120 |
| 7 | 5967561600 |
| 8 | 424097856000 |
| 9 | 34162713446400 |
| 10 | 3075990524006400 |
| 11 | 306135476264217600 |
| 12 | 33371339479827148800 |
| 13 | 3954242643911239680000 |
| 14 | 506046613478104258560000 |
| 15 | 69560546966425756200960000 |
| 16 | 10221346459144248675287040000 |
[1,4,56,1320,43680,1860480,96909120,5967561600, 424097856000,34162713446400,3075990524006400, 306135476264217600,33371339479827148800, 3954242643911239680000,506046613478104258560000, 69560546966425756200960000, 10221346459144248675287040000] |