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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 206 |
| 4 | 1813 |
| 5 | 17030 |
| 6 | 167229 |
| 7 | 1695920 |
| 8 | 17624932 |
| 9 | 186722580 |
| 10 | 2009077416 |
| 11 | 21894695420 |
| 12 | 241170873096 |
| 13 | 2680761546396 |
| 14 | 30032284769832 |
| 15 | 338744791093796 |
| 16 | 3843699928567438 |
| 17 | 43844993166845920 |
| 18 | 502497843180361288 |
| 19 | 5783367971991398760 |
| 20 | 66815895492710846218 |
[1,4,26,206,1813,17030,167229,1695920,17624932, 186722580,2009077416,21894695420,241170873096, 2680761546396,30032284769832,338744791093796, 3843699928567438,43844993166845920, 502497843180361288,5783367971991398760, 66815895492710846218] |