设第n项为an
a1=3/5=(1+2)/(3×1+2)
a2=4/8=(2+2)/(3×2+2)
a3=5/11=(3+2)/(3×3+2)
a4=6/14=(4+2)/(3×4+2)
a5=7/17=(5+2)/(3×5+2)
……
an=(n+2)/(3n+2)
数列的通项公式为an=(n+2)/(3n+2)