RSolve[ y[n] == 2 y[4 Sqrt[n]] + Log2[n], y, n ]
RSolve[ y[n] == 2 y[4 Sqrt[n]] + Log2[n], y, n ]; DiscretePlot[Evaluate[y[n] /. First[%] /. C[1] -> 0], {n, 50, 500}, AxesOrigin -> {0, 0}]