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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 8 |
| 3 | 60 |
| 4 | 312 |
| 5 | 2030 |
| 6 | 11752 |
| 7 | 74174 |
| 8 | 450292 |
| 9 | 2829898 |
| 10 | 17572000 |
| 11 | 110733420 |
| 12 | 695885000 |
| 13 | 4403631638 |
| 14 | 27874477216 |
| 15 | 177101756296 |
| 16 | 1126506215424 |
| 17 | 7182056699722 |
| 18 | 45847087891480 |
| 19 | 293141734241436 |
| 20 | 1876495434801400 |
| 21 | 12026885684352138 |
| 22 | 77161051350902456 |
| 23 | 495534832203481122 |
[2,8,60,312,2030,11752,74174,450292,2829898, 17572000,110733420,695885000,4403631638, 27874477216,177101756296,1126506215424, 7182056699722,45847087891480,293141734241436, 1876495434801400,12026885684352138, 77161051350902456,495534832203481122] |