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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 4 |
| 4 | 16 |
| 5 | 60 |
| 6 | 218 |
| 7 | 778 |
| 8 | 2744 |
| 9 | 9600 |
| 10 | 33391 |
| 11 | 115638 |
| 12 | 399137 |
| 13 | 1374050 |
| 14 | 4720272 |
| 15 | 16187632 |
| 16 | 55434424 |
| 17 | 189607406 |
| 18 | 647872199 |
| 19 | 2211794804 |
| 20 | 7545239986 |
| 21 | 25722676402 |
| 22 | 87641357150 |
| 23 | 298456587038 |
| 24 | 1015914399813 |
| 25 | 3456670564220 |
| 26 | 11757143968393 |
| 27 | 39976448714086 |
| 28 | 135887220346719 |
[1,4,16,60,218,778,2744,9600,33391,115638,399137, 1374050,4720272,16187632,55434424,189607406, 647872199,2211794804,7545239986,25722676402, 87641357150,298456587038,1015914399813, 3456670564220,11757143968393,39976448714086, 135887220346719] |