10 LET n=0: LET p=0
20 INPUT "Enter number: ";n
30 IF n>1 THEN GO SUB 1000
40 IF p=0 THEN PRINT n;" is not prime!"
50 IF p<>0 THEN PRINT n;" is prime!"
60 GO TO 10
1000 REM ***************
1001 REM * PRIME CHECK *
1002 REM ***************
1010 LET p=0
1020 IF n/2=INT (n/2) THEN RETURN
1030 LET p=1
1040 FOR i=3 TO SQR (n) STEP 2
1050 IF n/i=INT (n/i) THEN LET p=0: LET i= SQR (n)
1060 NEXT i
1070 RETURN