body  {
  background: #333;
}
canvas {
  position: relative;
  margin: 0 auto;
  display: block;
}

var rc = 0,
  seed = 30,
  MAX_RAND = 0xffffff;

function idxRand(nth) {
  if (nth != null) rc = nth;
  rc++;
  return Math.abs(Math.sin(seed * rc) * MAX_RAND);
}

var firstFour = [idxRand(), idxRand(), idxRand(), idxRand()],
  second = idxRand(1),
  fourth = idxRand(3);

console.log(firstFour);
console.log(second);
console.log(fourth);

var canvas = document.createElement("canvas"),
  c = canvas.getContext("2d");

canvas.width = 400;
canvas.height = 300;
c.fillStyle = "black";
c.fillRect(0, 0, canvas.width, canvas.height);
document.body.appendChild(canvas);

for (var i = 0; i < 300; i++) {
  c.fillStyle = "red";
  c.fillRect(idxRand() % 200, i, 4, 4);

  c.fillStyle = "green";
  c.fillRect(200 + Math.random() * 200, i, 4, 4);
}