It's referencing the Math Stack Exchange question which asked the same question: https://math.stackexchange.com/questions/885879/meaning-of-rays-in-polar-plot-o

It's referencing the Math Stack Exchange question which asked the same question: https://math.stackexchange.com/questions/885879/meaning-of-rays-in-polar-plot-of-prime-numbers/885894 https://math.stackexchange.com/questions/885879/meaning-of-r...