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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 38 |
| 3 | 210 |
| 4 | 1416 |
| 5 | 9199 |
| 6 | 60206 |
| 7 | 393585 |
| 8 | 2575161 |
| 9 | 16853437 |
| 10 | 110272832 |
| 11 | 721534069 |
| 12 | 4721192123 |
| 13 | 30892105126 |
| 14 | 202135973690 |
| 15 | 1322631911588 |
| 16 | 8654346869839 |
| 17 | 56627813612708 |
| 18 | 370531619063820 |
| 19 | 2424491930970999 |
| 20 | 15864128119739556 |
[4,38,210,1416,9199,60206,393585,2575161,16853437, 110272832,721534069,4721192123,30892105126, 202135973690,1322631911588,8654346869839, 56627813612708,370531619063820,2424491930970999, 15864128119739556] |