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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 160 |
| 5 | 1456 |
| 6 | 15904 |
| 7 | 202672 |
| 8 | 2951680 |
| 9 | 48361216 |
| 10 | 880405504 |
| 11 | 17630351872 |
| 12 | 385148108800 |
| 13 | 9114999832576 |
| 14 | 232311251144704 |
| 15 | 6343764407375872 |
| 16 | 184778982658539520 |
| 17 | 5718564661248065536 |
| 18 | 187389427488113557504 |
| 19 | 6481629887083387420672 |
| 20 | 235993351028007334051840 |
[1,1,4,22,160,1456,15904,202672,2951680,48361216, 880405504,17630351872,385148108800,9114999832576, 232311251144704,6343764407375872, 184778982658539520,5718564661248065536, 187389427488113557504,6481629887083387420672, 235993351028007334051840] |