/* A twin prime is a prime number that differs from another prime number by two. Write a function called isTwinPrime which takes an integer and returns true if it is a twin prime, or false if it is not.
Example:

5 is a prime, and 5 + 2 = 7, which is also a prime, so returns true.
9 is not a prime, and so does not need checking, so it returns false.
7 is a prime, but 7 + 2 = 9, which is not a prime. However, 7 - 2 = 5, which is a prime, so it returns true.
23 is a prime, but 23 + 2 is 25, which is not a prime.  23 - 2 is 21, which isn't a prime either, so 23 is not a twin prime.*/

function isTwinPrime(n) {
function isPrime(num) {
    for (let i = 2; i <= Math.sqrt(num); i++) {
      if (num % i === 0) return false;
    }
    return num >= 2;
  }
  return (isPrime(n) && (isPrime(n - 2) || isPrime(n + 2)));
}