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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 276 |
| 5 | 10688 |
| 6 | 1601952 |
| 7 | 892341888 |
| 8 | 1799786093088 |
| 9 | 13042490003160192 |
| 10 | 341378170022783017472 |
| 11 | 32526326484972756063585792 |
| 12 | 11367103329997359707194173746176 |
| 13 | 14669222110846093400698801891700529152 |
[1,4,20,276,10688,1601952,892341888,1799786093088, 13042490003160192,341378170022783017472, 32526326484972756063585792, 11367103329997359707194173746176, 14669222110846093400698801891700529152] |