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


val .isPrime = f(.i) {
    val .n = abs(.i)
    if .n <= 2: return .n == 2
 
    val .chkdiv = f(.n, .i) {
        if .i x .i <= .n {
            return .n ndiv .i and self(.n, .i+2)
        }
        return true
    }
 
    return .n ndiv 2 and .chkdiv(.n, 3)
}
 
writeln where .isPrime, series 100