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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 68 |
| 5 | 243 |
| 6 | 976 |
| 7 | 3770 |
| 8 | 15801 |
| 9 | 63897 |
| 10 | 274579 |
| 11 | 1145669 |
| 12 | 5007818 |
| 13 | 21350852 |
| 14 | 94536191 |
| 15 | 409707470 |
| 16 | 1831505449 |
| 17 | 8037909424 |
| 18 | 36209159140 |
| 19 | 160512573672 |
| 20 | 727565190083 |
| 21 | 3251708293128 |
| 22 | 14815146153312 |
| 23 | 66663538157045 |
| 24 | 305045223894040 |
| 25 | 1380476950480405 |
| 26 | 6340330378722993 |
| 27 | 28833396075309376 |
[1,2,6,18,68,243,976,3770,15801,63897,274579, 1145669,5007818,21350852,94536191,409707470, 1831505449,8037909424,36209159140,160512573672, 727565190083,3251708293128,14815146153312, 66663538157045,305045223894040,1380476950480405, 6340330378722993,28833396075309376] |