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A053491 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 112 |
| 5 | 960 |
| 6 | 10848 |
| 7 | 141120 |
| 8 | 2122496 |
| 9 | 36094464 |
| 10 | 685578240 |
| 11 | 14385761280 |
| 12 | 330532435968 |
| 13 | 8253827112960 |
| 14 | 222587077558272 |
| 15 | 6447285982126080 |
| 16 | 199630453605335040 |
| 17 | 6580280144225894400 |
| 18 | 230056747973625249792 |
| 19 | 8503148524089755566080 |
[1,0,4,12,112,960,10848,141120,2122496,36094464, 685578240,14385761280,330532435968,8253827112960, 222587077558272,6447285982126080, 199630453605335040,6580280144225894400, 230056747973625249792,8503148524089755566080] |