10 LET I=21
20 LET J=2
30 FOR K=-PI TO PI STEP 0.07
40 PLOT 21+I*SIN K,22+21*COS K
50 PLOT 21+21*SIN K,22+(I-1)*COS K
60 NEXT K
70 LET I=I-J
80 LET J=J+1
90 IF I>0 THEN GOTO 30