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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 3 |
| 4 | 4 |
| 5 | 23 |
| 6 | 66 |
| 7 | 280 |
| 8 | 1030 |
| 9 | 4207 |
| 10 | 16852 |
| 11 | 69747 |
| 12 | 289950 |
| 13 | 1222540 |
| 14 | 5192344 |
| 15 | 22239672 |
| 16 | 95864902 |
| 17 | 415730735 |
| 18 | 1812177000 |
| 19 | 7936353049 |
| 20 | 34901789568 |
| 21 | 154067755503 |
| 22 | 682428824890 |
| 23 | 3032173906692 |
| 24 | 13510960371744 |
| 25 | 60360526255204 |
| 26 | 270311970889296 |
| 27 | 1213232586744900 |
| 28 | 5456560663318648 |
[1,0,3,4,23,66,280,1030,4207,16852,69747,289950, 1222540,5192344,22239672,95864902,415730735, 1812177000,7936353049,34901789568,154067755503, 682428824890,3032173906692,13510960371744, 60360526255204,270311970889296,1213232586744900, 5456560663318648] |