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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 34 |
| 4 | 218 |
| 5 | 1386 |
| 6 | 8810 |
| 7 | 56010 |
| 8 | 356074 |
| 9 | 2263690 |
| 10 | 14391082 |
| 11 | 91489226 |
| 12 | 581629546 |
| 13 | 3697625866 |
| 14 | 23507122602 |
| 15 | 149443138122 |
| 16 | 950063174890 |
| 17 | 6039889469834 |
| 18 | 38397725300778 |
| 19 | 244107994962122 |
| 20 | 1551881335096170 |
| 21 | 9865861536380938 |
[0,6,34,218,1386,8810,56010,356074,2263690, 14391082,91489226,581629546,3697625866, 23507122602,149443138122,950063174890, 6039889469834,38397725300778,244107994962122, 1551881335096170,9865861536380938] |