Let $$O$$ be the centre of the circle $$𝑥^2 + 𝑦^2 = 𝑟^2$$, where $$𝑟 > \frac{\sqrt{5}}{2}$$. Suppose PQ is a chord of this circle and the equation of the line passing through P and Q is $$2𝑥 + 4𝑦 = 5$$. If the centre of the circumcircle of the triangle $$OPQ$$ lies on the line $$𝑥 + 2𝑦 = 4$$, then the value of 𝑟 is _____