TwinPrime.js

import { PrimeCheck } from './PrimeCheck'

/**
 * @function twinPrime
 * Gets the 'twin prime' of a prime number.
 *
 * @param {Integer} n The number to find the twin prime of.
 * @returns {Integer} Either the twin, or -1 if n or n + 2 is not prime.
 *
 * @see https://en.wikipedia.org/wiki/Twin_prime
 *
 * @example twinPrime(5) = 7
 * @example twinPrime(4) = -1
 */
function twinPrime(n) {
 const prime = PrimeCheck(n)

 if (!prime) {
 return -1
 }

 if (!PrimeCheck(n + 2)) {
 return -1
 }

 return n + 2
}

export { twinPrime }