a_n= \frac{2n-6}{n+3}
a_1= \frac{2*1-6}{1+3}=\frac{-4}{4}=-1
a_2= \frac{2*2-6}{2+3}=-\frac{2}{5}
a_3= \frac{2*3-6}{3+3}=0
a_4= \frac{2*4-6}{4+3}=\frac{2}{7}
a_5= \frac{2*5-6}{5+3}=\frac{4}{8}=\frac{1}{2}
…
a_n=(-2)^n-1
a_1=(-2)^1-1=-2-1=-3
a_2=(-2)^2-1=4-1=3
a_3=(-2)^3-1=-8-1=-9
a_4=(-2)^4-1=16-1=15
a_5=(-2)^5-1=-32-1=-33