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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 24 |
| 3 | 168 |
| 4 | 1120 |
| 5 | 8640 |
| 6 | 66816 |
| 7 | 529920 |
| 8 | 4212736 |
| 9 | 33632256 |
| 10 | 268713984 |
| 11 | 2148630528 |
| 12 | 17184194560 |
| 13 | 137456517120 |
| 14 | 1099579785216 |
| 15 | 8796367749120 |
| 16 | 70369826308096 |
| 17 | 562954298720256 |
| 18 | 4503616874348544 |
| 19 | 36028866141093888 |
| 20 | 288230651566489600 |
| 21 | 2305844111946547200 |
[1,6,24,168,1120,8640,66816,529920,4212736, 33632256,268713984,2148630528,17184194560, 137456517120,1099579785216,8796367749120, 70369826308096,562954298720256,4503616874348544, 36028866141093888,288230651566489600, 2305844111946547200] |