Array. Using p5.library.

array.js

var nums = [600, 500, 400, 300, 200, 100];

function setup() {
  createCanvas(648, 648);
}

function draw() {
background(random(85, 170), random(85, 170), random(85, 170));
stroke(random(85, 170), random(85, 170), random(85, 170), 100);
strokeWeight(60);
  for (i = 0; i < 6; i++) {
    fill(random(85, 170), random(85, 170), random(85, 170));
    ellipse(100 * i, 324, nums[i], nums[i]);
  }
  // frame rate may be set to a higher value depending upon graphics performance
  frameRate(5);
}