Solutions
Solution 1 (Click to Show/Hide)
function isSemiPrime(n) {
if (n <= 3) return false;
var ans = [];
var done = false;
while (!done) {
if (n % 2 === 0) {
ans.push(2);
n /= 2;
continue;
}
if (n % 3 === 0) {
ans.push(3);
n /= 3;
continue;
}
if (n === 1) return ans.length == 2;
var sr = Math.sqrt(n);
done = true;
// try to divide the checked number by all numbers till its square root.
for (var i = 6; i <= sr; i += 6) {
if (n % (i - 1) === 0) {
// is n divisible by i-1?
ans.push(i - 1);
n /= i - 1;
done = false;
break;
}
if (n % (i + 1) === 0) {
// is n divisible by i+1?
ans.push(i + 1);
n /= i + 1;
done = false;
break;
}
}
}
ans.push(n);
return ans.length == 2;
}