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


    PRINT "ENTER A NUMBER "
    INPUT P
    GOSUB 100
    IF Z = 1 THEN PRINT "It is prime."
    IF Z = 0 THEN PRINT "It isn't prime."
    END
 
100 REM PRIMALITY OF THE NUMBER P BY TRIAL DIVISION
    IF P < 2 THEN RETURN
    LET Z = 1
    IF P < 4 THEN RETURN
    LET I = 2
110 IF (P/I)*I = P THEN LET Z = 0
    IF Z = 0 THEN RETURN
    LET I = I + 1
    IF I*I <= P THEN GOTO 110
    RETURN