Problem 7
By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
What is the 10001st prime number?
Solution
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<!–
By listing the first six prime numbers:
2, 3, 5, 7, 11, and 13, we can see that
the 6th prime is 13.
What is the 10001st prime number?
–>
<head>
<title>Project Euler 007</title>
</head>
<body>
<script type="text/javascript">
maxPrime = 10001;
primes = new Array(maxPrime);
primes[0] = 2;
primes[1] = 3;
primeCount = 2;
while (primeCount < maxPrime) {
isPrime = false;
candidate = primes[primeCount – 1] + 2;
while (!isPrime) {
isPrime = true;
for (pindex = 0; pindex < primeCount; pindex++) {
prime = primes[pindex];
if (candidate % prime == 0) {
isPrime = false;
break;
}
}
if (!isPrime) { candidate += 2; }
else {
primes[primeCount] = candidate;
primeCount++;
}
}
}
document.write("<b>" + primes[maxPrime-1] + "</b>");
</script>
</body>
</html>
Discussion
Happy JavaScript nth prime finder.
If you have any questions, leave a comment, find me on Twitter (@azzlsoft) or email (rich@azzlsoft.com).
azzlsoft.com 