Eratosthenes

function sieveOfEratosthenes(max) {

  let isPrimeNumber = new Array(max + 1).fill(true);

​

  isPrimeNumber[0] = false;

  isPrimeNumber[1] = false;

​

  for (let k = 2; k < Math.sqrt(max); k++) {

    if (isPrimeNumber[k])

      for (n = 2 * k; n <= max; n += k) isPrimeNumber[n] = false;

  }

​

  return isPrimeNumber;

}

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  background(0);

  fill(255);

  noStroke();

  let step = 12;

  let l = Math.floor(( min(width, height)/2 - step ) / step);

  let k = 2*l+1;

  let isPrimeNumber = sieveOfEratosthenes(k*k);

  translate(width/2 - (l+1)*step, height/2 - (l)*step);

  for (let y=0; y<k; y++)

    for(let x=1; x<=k; x++) {

      if (isPrimeNumber[y*k+x])

        circle(x*step, y*step, step-2);

      else

        circle(x*step, y*step, step/4);

    }

}

​

function draw() {

}