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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 952 |
| 7 | 2800 |
| 8 | 8132 |
| 9 | 23608 |
| 10 | 67884 |
| 11 | 195132 |
| 12 | 556932 |
| 13 | 1588836 |
| 14 | 4507524 |
| 15 | 12782560 |
| 16 | 36088224 |
| 17 | 101845032 |
| 18 | 286372148 |
| 19 | 804930196 |
| 20 | 2255624360 |
| 21 | 6318588308 |
| 22 | 17654567968 |
[1,4,12,36,108,324,952,2800,8132,23608,67884, 195132,556932,1588836,4507524,12782560,36088224, 101845032,286372148,804930196,2255624360, 6318588308,17654567968] |