How to draw 1 O- triangle, 4 O- crosses and 9 O's in the second grade of primary school, followed by 16?
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According to figure 1 (viewed horizontally), the number of circles is 0 10, figure 2 is 12 1 and figure 3 is 252, so the middle of figure 4 should be 1+2=3, 2+3 = 5,3.