Georg Cantor defined infinity as the size of the never-ending list of counting numbers.
BBC Radio 4
If the square root of +1 is both +1 and -1, then what is the square root of -1?
The ratio of consecutive numbers in the Fibonacci is close to 1.618, the Golden Ratio.
At its simplest, Pi is the ratio of the circumference of a circle to its diameter.
Strangely, 'nothing' had to be invented, and then it took thousands of years to catch on.