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<!DOCTYPE html>
<html>
<head>
<title>How many bit-reversed primes are prime?</title>
</head>
<body>
<pre>
<noscript><p>Javascript is disabled</p></noscript>
<script>
var start = new Date().getTime();

// Add the lpad method to Strings, for adding left padding
String.prototype.lpad = function(padString, length) {
    var str = this;
    while (str.length < length)
        str = padString + str;
    return str;
}

// Naive prime checker
function is_prime(n)
{
    for (var i = 2; i <= n/2; i++) {
        if (n % i === 0) {
            return false;
        }
    }
    if (n === 1) {
        return false;
    }
    return true;
}

// Bit reversal
function bit_reverse(num)
{
    var rev = 0;
    while (num > 0) {
        rev <<= 1;
        rev |= (num & 1);
        num >>= 1;
    }
    return rev;
}

for (var num = 1; num < 10000; num++) {
    var rev = bit_reverse(num);
    var num_prime = is_prime(num);
    var rev_prime = is_prime(rev);

    document.write(num.toString().lpad(" ", 7) + " ");
    document.write(num_prime ? "Prime" : "     ");
    document.write("  ");

    document.write(rev.toString().lpad(" ", 7) + " ");
    document.write(rev_prime ? "Prime" : "     ");
    document.write("  ");

    document.write(num_prime && rev_prime ? "(both)" : "");
    document.write("\n");
}

var end = new Date().getTime();
var time = end - start;
document.write('Execution time: ' + time + '\n');

</script>
</pre>
</body>
</html>