100 PRINT "NUMBER TO BE FACTORED?"
110 INPUT N
120 PRINT
130 IF N = 0 THEN GOTO 999
140 IF N = 2 THEN 250
150 LET Z = 0
170 LET F = 2
180 GOSUB 300
185 IF N = 1 THEN 500
190 FOR F = 3 TO SQR(N)+1 STEP 2
200     GOSUB 300
205     IF N = 1 THEN 500
210 NEXT F
220 IF Z = 0 THEN 250
230 PRINT N;
240 GOTO 500
250 PRINT N; "IS PRIME."
260 GOTO 500
300 REM TESTS F AS A FACTOR.
310 IF N/F <> INT(N/F) THEN 400
330 IF Z > 0 THEN GOTO 370
340 PRINT N; "HAS THE FACTORS :"
350 PRINT "      "
360 LET Z = 1
370 PRINT F;
380 LET N = N/F
390 IF N <> 1 THEN 310
400 RETURN
500 REM ALL DONE.
510 PRINT
520 PRINT
530 PRINT
540 GOTO 100
999 END