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


   DO n = 1, 1E6
     Euler = n^2 + n + 41
     IF( Prime(Euler) == 0 ) WRITE(Messagebox) Euler, ' is NOT prime for n =', n
   ENDDO                            ! e.g.    1681 = 40^2 + 40 + 41 is NOT prime
END
 
FUNCTION Prime(number)
   Prime = number == 2
   IF( (number > 2) * MOD(number,2) ) THEN
     DO i = 3, number^0.5, 2
       IF(MOD(number,i) == 0) THEN
         Prime = 0
         RETURN
       ENDIF
     ENDDO
     Prime = 1
   ENDIF
END