primeTester

/**
 * A prime number is a whole number that has no other divisors other than
 * itself and 1. Write a function that accepts a number and returns true if it's
 * a prime number, false if it's not.
 */

var primeTester = function(n) { 

  if( n === 1) return false;

  var limit = Math.ceil(Math.sqrt(n));
  for(var i = limit; i > 1; i--){
      if(n%i === 0) return false;
  }

  return true

};

/* Extra credit: Write a function that generates a list of all prime numbers
 * in a user-specified range (inclusive). If you're not quite sure where to start,
 * check out the Sieve of Eratosthenes on Wikipedia. (And if you're feeling
 * saucy, check out the Sieve of Atkin.)
 */

var primeSieve = function(start, end) {
  // Return a list of all prime numbers >= start and <= end
  var primes = [];
  var markers = Array(end); //inclusive
  for(var i =2; i < end; i++){
    if(markers[i]===undefined){
      if(i >= start) primes.push(i);
      for(var j = i*i; j < markers.length; j+=i){
        markers[j] = "Not prime";
      }
    }
  }
  return primes;
};