Algorithm for calculating hash collision probability

collision.js

const calculate = (n, k) => {
  const exponent = (-k * (k - 1)) / (2 * n)
  return 1 - Math.E ** exponent
}

// where `n` is the number of possible unique hashes
// where `k` is the number of values created

// calculate(100000, 25) => 0.0029955044966269995 aka 0.29% chance of collision