Dots pattern

hi i am trying to emulate this image - original file here - https://www.math.cuhk.edu.hk/sites/default/files/about-us/newsletter/newsletter1718.pdf

I specifically want the disappearing dots from small to large to small again. i tried with the blend tool but i can't make it perfect like this

also there are lots of gradient overlaps which I can't seem to understand. maybe someone can give me a hand.