10 READ N
20 FOR I = 1 TO N-1
30     FOR J = 1 TO N-1
40         LET P(I,J) = I*J - INT(I*J/N)*N
50     NEXT J
60 NEXT I
70 FOR I = 1 TO N-1
80     FOR J = 1 TO N-1
90         IF P(I,J) = 1 THEN 140
100    NEXT J
110    PRINT I;"DOES NOT HAVE AN INVERSE"
120 NEXT I
130 STOP
140 PRINT I;"HAS AS INVERSE " J
150 GOTO 120
160 DATA 7
170 END
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