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<!DOCTYPE html>
<html>
<head>
<title>How many bit-reversed primes are prime?</title>
</head>
<body>
<pre>
<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;
}
}
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>
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