Thank you for your post! Indeed pi is a constant.
The Aristotle-Hawking side of the forum goes "yawn" - and dumps it into the anthropic principle with all the other mysterious constants, 'nuff said.
Meanwhile, the Plato-Penrose side of the forum wonder at the geometry. The mathematicians discovered circles - and their properties, they say, they sure didn't invent them. They were already there. But why? And why is it universal, the same everywhere?
As far as mathemtics goes, a number is basically just a metaphysical construct. Any sort of a metaphysical construct is about as real as there is anything in the real world to which it corresponds. Thus integers correspond to God's invention of fingers and toes, rational numbers and fractions correspond to the invention of knives, negative numbers correspond the the invention of the idea of debt, imaginary numbers correspond to solutions of differential equations and the relationships between exponential functions and ordinary sines and cosines etc. etc.
There isn't any sort of mathematics which corresponds to evolutionism. That's basically the realm of pure fiction.