JSFiddle - React, Tailwind, and code Playground

JavaScript

let estPremier = (n) => {
	if (n < 2) {
  	return false;
  }
  if (n === 2) {
  	return true;
  }
  for (let i = 2; i <= Math.sqrt(n); ++i) {
  	if (n % i === 0) {
    	return false;
    }
  }
  return true;
};

let nbNb, nbNbPremiers = 0;
for(nbNb = 0; nbNb * nbNb - nbNb + 41 < 10000000; ++nbNb) {
	if (estPremier(nbNb * nbNb - nbNb + 41)) {
  	++nbNbPremiers;
  }
}
alert(nbNbPremiers / nbNb);