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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 20 |
| 4 | 88 |
| 5 | 368 |
| 6 | 1504 |
| 7 | 6080 |
| 8 | 24448 |
| 9 | 98048 |
| 10 | 392704 |
| 11 | 1571840 |
| 12 | 6289408 |
| 13 | 25161728 |
| 14 | 100655104 |
| 15 | 402636800 |
| 16 | 1610579968 |
| 17 | 6442385408 |
| 18 | 25769672704 |
| 19 | 103078952960 |
| 20 | 412316336128 |
| 21 | 1649266393088 |
| 22 | 6597067669504 |
| 23 | 26388274872320 |
[0,4,20,88,368,1504,6080,24448,98048,392704, 1571840,6289408,25161728,100655104,402636800, 1610579968,6442385408,25769672704,103078952960, 412316336128,1649266393088,6597067669504, 26388274872320] |