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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 318 |
| 6 | 936 |
| 7 | 2760 |
| 8 | 8136 |
| 9 | 23976 |
| 10 | 70662 |
| 11 | 208260 |
| 12 | 613788 |
| 13 | 1808964 |
| 14 | 5331420 |
| 15 | 15712878 |
| 16 | 46309320 |
| 17 | 136483800 |
| 18 | 402247944 |
| 19 | 1185513624 |
| 20 | 3493970742 |
| 21 | 10297504260 |
| 22 | 30349021740 |
| 23 | 89445276900 |
| 24 | 263615006412 |
| 25 | 776931706398 |
[1,4,12,36,108,318,936,2760,8136,23976,70662, 208260,613788,1808964,5331420,15712878,46309320, 136483800,402247944,1185513624,3493970742, 10297504260,30349021740,89445276900,263615006412, 776931706398] |