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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 24 |
| 4 | 312 |
| 5 | 4720 |
| 6 | 82800 |
| 7 | 1662024 |
| 8 | 37665152 |
| 9 | 952401888 |
| 10 | 26602156800 |
| 11 | 813815035000 |
| 12 | 27069937855488 |
| 13 | 972940216546896 |
| 14 | 37581134047987712 |
| 15 | 1552687346633913000 |
| 16 | 68331503866677657600 |
| 17 | 3191386068123595166656 |
| 18 | 157663539876436721860608 |
[0,2,24,312,4720,82800,1662024,37665152,952401888, 26602156800,813815035000,27069937855488, 972940216546896,37581134047987712, 1552687346633913000,68331503866677657600, 3191386068123595166656,157663539876436721860608] |