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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 56 |
| 3 | 504 |
| 4 | 2024 |
| 5 | 8064 |
| 6 | 18200 |
| 7 | 50736 |
| 8 | 99248 |
| 9 | 202688 |
| 10 | 343256 |
| 11 | 657904 |
| 12 | 983008 |
| 13 | 1708672 |
| 14 | 2485968 |
| 15 | 3755184 |
| 16 | 5289944 |
| 17 | 8069736 |
| 18 | 10539792 |
| 19 | 15387320 |
| 20 | 19913840 |
[4,56,504,2024,8064,18200,50736,99248,202688, 343256,657904,983008,1708672,2485968,3755184, 5289944,8069736,10539792,15387320,19913840] |