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


prime?: func [n] [
    case [
        n = 2 [ true  ]
        n <= 1 or (n // 2 = 0) [ false ]
        true [
            for i 3 round square-root n 2 [
                if n // i = 0 [ return false ]
            ]
            true
        ]
    ]
]