Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


import std.stdio, std.algorithm, std.range, std.math;
 
bool isPrime1(in int n) pure nothrow {
    if (n == 2)
        return true;
    if (n <= 1 || (n & 1) == 0)
        return false;
 
    for(int i = 3; i <= real(n).sqrt; i += 2)
        if (n % i == 0)
            return false;
    return true;
}
 
void main() {
    iota(2, 40).filter!isPrime1.writeln;
}