https://www.wikiwand.com/en/Sierpinski_triangle

RecursiveEllipsesSierpinskiTriangle.pde

void setup() {
  size(1200,1200,P3D);
  smooth(8);
  frameRate(60);
  hint(DISABLE_OPTIMIZED_STROKE);
  colorMode(HSB, 360, 360, 360);
}

void draw() {
  background(0);
  drawCircles(width/2, height/2, 600);
  saveFrame("frames/cir-######.png");
}

void drawCircles(float x, float y, float radius) {
  stroke(random(1,359),random(1,359),random(1,359),255);
  strokeWeight(1);
  noFill();
  ellipse(x, y, radius, radius);
  // try adjusting radius 2...12
  if (radius > 8) {
    drawCircles(x + radius/2, y, radius/2);
    drawCircles(x - radius/2, y, radius/2);
    drawCircles(x, y + radius/2, radius/2);
    // uncomment for added fun
    //drawCircles(x, y - radius/2, radius/2);
  }
}