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


FUNCTION prime% (n!)
  STATIC i AS INTEGER
  IF n = 2 THEN
    prime = 1
  ELSEIF n <= 1 OR n MOD 2 = 0 THEN
    prime = 0
  ELSE
    prime = 1
    FOR i = 3 TO INT(SQR(n)) STEP 2
      IF n MOD i = 0 THEN
        prime = 0
        EXIT FUNCTION
      END IF
    NEXT i
  END IF
END FUNCTION
 
' Test and display primes 1 .. 50
DECLARE FUNCTION prime% (n!)
FOR n = 1 TO 50
  IF prime(n) = 1 THEN PRINT n;
NEXT n