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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 168 |
| 4 | 1280 |
| 5 | 10296 |
| 6 | 86016 |
| 7 | 739024 |
| 8 | 6488064 |
| 9 | 57946200 |
| 10 | 524812288 |
| 11 | 4808643120 |
| 12 | 44493176832 |
| 13 | 415146189360 |
| 14 | 3901709352960 |
| 15 | 36902658748320 |
| 16 | 350980432461824 |
| 17 | 3354743017001880 |
| 18 | 32207616155320320 |
| 19 | 310446853795570800 |
| 20 | 3003167577200394240 |
| 21 | 29146910264615460240 |
[1,4,24,168,1280,10296,86016,739024,6488064, 57946200,524812288,4808643120,44493176832, 415146189360,3901709352960,36902658748320, 350980432461824,3354743017001880, 32207616155320320,310446853795570800, 3003167577200394240,29146910264615460240] |