The first figure of the sierpinski triangle has one shaded triangle. The second figure of the sierpinski triangle has three shaded triangles. The third figure of the sierpinski triangle has nine shaded triangles. Which summation represents the total number of shaded triangles in the first 15 figures? sigma-summation underscript n = 1 overscript 15 endscripts 1 (3) superscript n minus 1 sigma-summation underscript n = 1 overscript 15 endscripts 3 (1) superscript n minus 1 sigma-summation underscript n = 1 overscript 15 endscripts 1 (one-third) superscript n minus 1 sigma-summation underscript n = 1 overscript 15 endscripts one-third (1) superscript n minus 1.