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


proc is_prime n {
    if {$n <= 1} {return false}
    if {$n == 2} {return true}
    if {$n % 2 == 0} {return false}
    for {set i 3} {$i <= sqrt($n)} {incr i 2} {
        if {$n % $i == 0} {return false}
    }
    return true
}