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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 128 |
| 6 | 704 |
| 7 | 3840 |
| 8 | 20992 |
| 9 | 114688 |
| 10 | 626688 |
| 11 | 3424256 |
| 12 | 18710528 |
| 13 | 102236160 |
| 14 | 558628864 |
| 15 | 3052404736 |
| 16 | 16678649856 |
| 17 | 91133837312 |
| 18 | 497964548096 |
| 19 | 2720928890880 |
| 20 | 14867431948288 |
| 21 | 81237158920192 |
| 22 | 443888091267072 |
| 23 | 2425449636429824 |
| 24 | 13252903275855872 |
[0,1,4,24,128,704,3840,20992,114688,626688, 3424256,18710528,102236160,558628864,3052404736, 16678649856,91133837312,497964548096, 2720928890880,14867431948288,81237158920192, 443888091267072,2425449636429824, 13252903275855872] |