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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 32 |
| 3 | 240 |
| 4 | 1808 |
| 5 | 13616 |
| 6 | 102544 |
| 7 | 772272 |
| 8 | 5816080 |
| 9 | 43801648 |
| 10 | 329875856 |
| 11 | 2484337584 |
| 12 | 18709866512 |
| 13 | 140906415920 |
| 14 | 1061184377488 |
| 15 | 7991916306096 |
| 16 | 60188151652624 |
| 17 | 453284726792752 |
| 18 | 3413745694159760 |
| 19 | 25709358766289328 |
| 20 | 193620494140664336 |
[4,32,240,1808,13616,102544,772272,5816080, 43801648,329875856,2484337584,18709866512, 140906415920,1061184377488,7991916306096, 60188151652624,453284726792752,3413745694159760, 25709358766289328,193620494140664336] |