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


BYTE FUNC IsPrime(CARD a)
  CARD i
 
  IF a<=1 THEN
    RETURN (0)
  FI
 
  FOR i=2 TO a/2
  DO
    IF a MOD i=0 THEN
      RETURN (0)
    FI
  OD
RETURN (1)
 
PROC Test(CARD a)
  IF IsPrime(a) THEN
    PrintF("%I is prime%E",a)
  ELSE
    PrintF("%I is not prime%E",a)
  FI
RETURN
 
PROC Main()
  Test(13)
  Test(997)
  Test(1)
  Test(6)
  Test(120)
  Test(0)
RETURN