Solution of $f(3x)=\frac{f(x)f(4x)}{2f(2x)}+\frac{f^2(2x)}{2f(x)}$?

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What are the analytic solutions to $f(3x)=\dfrac{f(x)f(4x)}{2f(2x)}+\dfrac{f^2(2x)}{2f(x)}$?

Are there solutions that do not satisfy a linear first or second ODE ?

See also : About the addition formula $f(x+y) = f(x)g(y)+f(y)g(x)$