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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 972 |
| 7 | 2916 |
| 8 | 8748 |
| 9 | 26244 |
| 10 | 78732 |
| 11 | 236196 |
| 12 | 708588 |
| 13 | 2125764 |
| 14 | 6377292 |
| 15 | 19131876 |
| 16 | 57395628 |
| 17 | 172186884 |
| 18 | 516560652 |
| 19 | 1549681956 |
| 20 | 4649045868 |
| 21 | 13947137604 |
| 22 | 41841412812 |
| 23 | 125524238436 |
| 24 | 376572715308 |
| 25 | 1129718145924 |
[1,4,12,36,108,324,972,2916,8748,26244,78732, 236196,708588,2125764,6377292,19131876,57395628, 172186884,516560652,1549681956,4649045868, 13947137604,41841412812,125524238436,376572715308, 1129718145924] |