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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 8 |
| 2 | 48 |
| 3 | 320 |
| 4 | 2176 |
| 5 | 14848 |
| 6 | 101376 |
| 7 | 692224 |
| 8 | 4726784 |
| 9 | 32276480 |
| 10 | 220397568 |
| 11 | 1504968704 |
| 12 | 10276569088 |
| 13 | 70172803072 |
| 14 | 479169871872 |
| 15 | 3271976550400 |
| 16 | 22342453428224 |
| 17 | 152563815022592 |
| 18 | 1041770892754944 |
| 19 | 7113656621858816 |
| 20 | 48575085832830976 |
| 21 | 331691433687777280 |
[2,8,48,320,2176,14848,101376,692224,4726784, 32276480,220397568,1504968704,10276569088, 70172803072,479169871872,3271976550400, 22342453428224,152563815022592,1041770892754944, 7113656621858816,48575085832830976, 331691433687777280] |