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


      FOR i% = -1 TO 100
        IF FNisprime(i%) PRINT ; i% " is prime"
      NEXT
      END
 
      DEF FNisprime(n%)
      IF n% <= 1 THEN = FALSE
      IF n% <= 3 THEN = TRUE
      IF (n% AND 1) = 0 THEN = FALSE
      LOCAL t%
      FOR t% = 3 TO SQR(n%) STEP 2
        IF n% MOD t% = 0 THEN = FALSE
      NEXT
      = TRUE