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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 52 |
| 4 | 228 |
| 5 | 1192 |
| 6 | 6160 |
| 7 | 33344 |
| 8 | 191380 |
| 9 | 1072232 |
| 10 | 6416600 |
| 11 | 35990544 |
| 12 | 212278256 |
| 13 | 1145811772 |
[1,4,12,52,228,1192,6160,33344,191380,1072232, 6416600,35990544,212278256,1145811772] |