Prime Palindrome

Prime Palindrome Javascript

var highEnd = 1000;
var primes = sieve(highEnd);
highEnd--;
var found = false;
while (found == false ) {
    if (isPalindrome(highEnd.toString()) == true) {
        if (primes[highEnd] == true) {
            found = true;
        }
    }
    highEnd--;
}
console.log(++highEnd);
function isPalindrome(input) {
    var i;
    var length = input.length -1;

    for (i=0; i< length; i++) {
        if (input[i] != input[length-i]) {
            return false;
        }
    }
   return true;
}
function sieve (highEnd) {
    var sieve = newFilledArray(highEnd, true);
    var maxCheck = Math.sqrt(highEnd);
    var i, j;
    var results = [];

    for (i = 2; i <= maxCheck; i++) {
        if (sieve[i] == true) {
            for (j = i * i; j < highEnd; j += i) {
                sieve[j] = false
            }
        }
    }
    for (i=2; i<highEnd; i++) {
        if  (sieve[i]==true) {
            results.push(i);
        }
    }
    return(sieve);
}
function newFilledArray(length, val) {
    var array = [];
    for (var i = 0; i < length; i++) {
        array[i] = val;
    }
    return array;
}

Prime Palindrome PHP

// first create a sieve containing all the prime numbers between
// 1 and 1000
$highEnd = 1000;
$maxCheck = sqrt($highEnd);
$sieve = array_fill(0,1000, true);

for ($i = 2; $i<= $maxCheck; $i++) {
    if ($sieve[$i] == true) {
        for ($j = $i * $i; $j < $highEnd; $j += $i) {
            $sieve[$j] = false;
            }
    }
}
// filter out all the non-primes
//$sieve = array_filter($sieve);

// starting at the largest prime in the sample
// loop backward until a palindrome is encountered
do {
    end($sieve);
    $key = (string) key($sieve);
    $value = array_pop($sieve);
    $length = strlen($key) -1;
    $found = false;
    if ($value) {
        $found = true;
        for ($i=0; $i< $length; $i++) {
            if ($key[$i] != $key[$length-$i]) {
                $found = false;
            }
        }
    }

} while (! $found);

echo $key;