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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 60 |
| 5 | 440 |
| 6 | 3710 |
| 7 | 34608 |
| 8 | 355992 |
| 9 | 4004880 |
| 10 | 48948570 |
| 11 | 646121080 |
| 12 | 9163171732 |
| 13 | 138974771208 |
| 14 | 2244977073430 |
| 15 | 38485321258720 |
| 16 | 697867158824880 |
| 17 | 13346709412525728 |
| 18 | 268504389357870642 |
| 19 | 5668425997555046760 |
| 20 | 125302048367006296940 |
| 21 | 2894477317277845459160 |
[0,0,2,8,60,440,3710,34608,355992,4004880, 48948570,646121080,9163171732,138974771208, 2244977073430,38485321258720,697867158824880, 13346709412525728,268504389357870642, 5668425997555046760,125302048367006296940, 2894477317277845459160] |