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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 20 |
| 3 | 75 |
| 4 | 389 |
| 5 | 1852 |
| 6 | 8485 |
| 7 | 41247 |
| 8 | 196946 |
| 9 | 931243 |
| 10 | 4464289 |
| 11 | 21314416 |
| 12 | 101500589 |
| 13 | 484945365 |
| 14 | 2314846870 |
| 15 | 11042132315 |
| 16 | 52714123333 |
| 17 | 251602109008 |
| 18 | 1200668947009 |
| 19 | 5730793024341 |
| 20 | 27351896253430 |
| 21 | 130538870872807 |
| 22 | 623034403841625 |
[4,20,75,389,1852,8485,41247,196946,931243, 4464289,21314416,101500589,484945365,2314846870, 11042132315,52714123333,251602109008, 1200668947009,5730793024341,27351896253430, 130538870872807,623034403841625] |