100 CLS: CURSOR 0

110 Z=32: S=1

120 FOR D=0 TO 100 STEP S

130 FOR C=110 TO 330 STEP S

140 A=0: B=0: N=0

150 IF N<Z GOTO 300

160 IF N=Z N=15

170 IF N>15 N=N-15

180 LINE N, 3*C-340, 100-D, 3*C-338, 100-D, 1

190 LINE N, 3*C-340, 100+D, 3*C-338, 100+D, 1

220 NEXT C

230 NEXT D

240 CURSOR 1

250 END

300 X=A*A: Y=B*B

310 P=X+Y

350 IF P<10000 GOTO 370

360 GOTO 160

370 F=(A*A-B*B)/50-220+C

380 B=A*B/25+D

390 A=F: N=N+1

400 GOTO 150