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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 16 |
| 5 | 57 |
| 6 | 160 |
| 7 | 484 |
| 8 | 1449 |
| 9 | 4250 |
| 10 | 12736 |
| 11 | 37980 |
| 12 | 112684 |
| 13 | 335528 |
| 14 | 998929 |
| 15 | 2971856 |
| 16 | 8844112 |
| 17 | 26318889 |
| 18 | 78319204 |
| 19 | 233069764 |
| 20 | 693574740 |
| 21 | 2063954658 |
| 22 | 6142018600 |
| 23 | 18277651737 |
| 24 | 54391278960 |
| 25 | 161859683044 |
| 26 | 481668191001 |
| 27 | 1433366397054 |
[0,4,6,16,57,160,484,1449,4250,12736,37980,112684, 335528,998929,2971856,8844112,26318889,78319204, 233069764,693574740,2063954658,6142018600, 18277651737,54391278960,161859683044,481668191001, 1433366397054] |