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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 14 |
| 4 | 60 |
| 5 | 252 |
| 6 | 1212 |
| 7 | 5880 |
| 8 | 30904 |
| 9 | 166976 |
| 10 | 952456 |
| 11 | 5587840 |
| 12 | 34217216 |
| 13 | 215204960 |
| 14 | 1401551376 |
| 15 | 9360467760 |
| 16 | 64384034784 |
| 17 | 453328282624 |
| 18 | 3274696185568 |
| 19 | 24173219998912 |
| 20 | 182546586425408 |
[1,4,14,60,252,1212,5880,30904,166976,952456, 5587840,34217216,215204960,1401551376,9360467760, 64384034784,453328282624,3274696185568, 24173219998912,182546586425408] |