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Problem 3: Largest prime factor

curriculum/challenges/english/blocks/project-euler-problems-1-to-100/5900f36f1000cf542c50fe82.md

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--description--

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the given number?

--hints--

largestPrimeFactor(2) should return a number.

js
assert.isNumber(largestPrimeFactor(2));

largestPrimeFactor(2) should return 2.

js
assert.strictEqual(largestPrimeFactor(2), 2);

largestPrimeFactor(3) should return 3.

js
assert.strictEqual(largestPrimeFactor(3), 3);

largestPrimeFactor(5) should return 5.

js
assert.strictEqual(largestPrimeFactor(5), 5);

largestPrimeFactor(7) should return 7.

js
assert.strictEqual(largestPrimeFactor(7), 7);

largestPrimeFactor(8) should return 2.

js
assert.strictEqual(largestPrimeFactor(8), 2);

largestPrimeFactor(13195) should return 29.

js
assert.strictEqual(largestPrimeFactor(13195), 29);

largestPrimeFactor(600851475143) should return 6857.

js
assert.strictEqual(largestPrimeFactor(600851475143), 6857);

--seed--

--seed-contents--

js
function largestPrimeFactor(number) {

  return true;
}

largestPrimeFactor(13195);

--solutions--

js
const largestPrimeFactor = (number) => {
  let largestFactor = number;

  for (let i = 2; i <= Math.sqrt(largestFactor); i++) {
    if (!(largestFactor % i)) {
      let factor = largestFactor / i;
      let candidate = largestPrimeFactor(factor);

      return i > candidate ? i : candidate;
    }
  }

  return largestFactor;
}