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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 22 |
| 5 | 54 |
| 6 | 522 |
| 7 | 2376 |
| 8 | 15236 |
| 9 | 82512 |
| 10 | 483332 |
| 11 | 2728296 |
| 12 | 15667920 |
| 13 | 89257896 |
| 14 | 510388840 |
| 15 | 2913416640 |
| 16 | 16643861824 |
| 17 | 95047963488 |
| 18 | 542884234608 |
| 19 | 3100533567552 |
| 20 | 17708509939040 |
| 21 | 101139309767520 |
| 22 | 577645632221792 |
[0,1,0,22,54,522,2376,15236,82512,483332,2728296, 15667920,89257896,510388840,2913416640, 16643861824,95047963488,542884234608, 3100533567552,17708509939040,101139309767520, 577645632221792] |