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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 20 |
| 3 | 84 |
| 4 | 340 |
| 5 | 1364 |
| 6 | 5460 |
| 7 | 21844 |
| 8 | 87380 |
| 9 | 349524 |
| 10 | 1398100 |
| 11 | 5592404 |
| 12 | 22369620 |
| 13 | 89478484 |
| 14 | 357913940 |
| 15 | 1431655764 |
| 16 | 5726623060 |
| 17 | 22906492244 |
| 18 | 91625968980 |
| 19 | 366503875924 |
| 20 | 1466015503700 |
| 21 | 5864062014804 |
| 22 | 23456248059220 |
| 23 | 93824992236884 |
[4,20,84,340,1364,5460,21844,87380,349524,1398100, 5592404,22369620,89478484,357913940,1431655764, 5726623060,22906492244,91625968980,366503875924, 1466015503700,5864062014804,23456248059220, 93824992236884] |