JavaScript function to get the most rectangular image dimension that fits a certain number of pixels with the least (or no) addition of extra pixels.

pixelsintorectangle.js

function pixelsIntoRect(n, k){
  var max = ~~Math.sqrt(n);
  return Array.from({length: max}, (_, i, a) => [n%(max-i), max-i])
              .sort((a, b) => a[0] - b[0])
              .slice(0, k)
              .map(t => [Math.ceil(n/t[1]), t[1], (Math.ceil(n/t[1])*t[1])-n])
              .filter(a => Math.round(a[1]/a[0]) == 1)
              .sort((a, b) => a[2] - b[2])
}

pixelsIntoRect(262144)