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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 12 |
| 5 | 30 |
| 6 | 72 |
| 7 | 162 |
| 8 | 356 |
| 9 | 766 |
| 10 | 1616 |
| 11 | 3378 |
| 12 | 7004 |
| 13 | 14406 |
| 14 | 29480 |
| 15 | 60090 |
| 16 | 122036 |
| 17 | 247150 |
| 18 | 499456 |
| 19 | 1007458 |
| 20 | 2029068 |
| 21 | 4081686 |
| 22 | 8202456 |
| 23 | 16469642 |
| 24 | 33046628 |
| 25 | 66271166 |
| 26 | 132836784 |
| 27 | 266160818 |
| 28 | 533127612 |
| 29 | 1067587174 |
| 30 | 2137374088 |
| 31 | 4278378970 |
[0,0,4,12,30,72,162,356,766,1616,3378,7004,14406, 29480,60090,122036,247150,499456,1007458,2029068, 4081686,8202456,16469642,33046628,66271166, 132836784,266160818,533127612,1067587174, 2137374088,4278378970] |