请仔细观察下列等式:a1=2×1+3=5,a2=2×2+3=7,a3=2×3+3=9,a4=2×4+3=11,…,则按此规律当an=4013是
问题描述:
请仔细观察下列等式:a1=2×1+3=5,a2=2×2+3=7,a3=2×3+3=9,a4=2×4+3=11,…,则按此规律当an=4013是
答
an=2n+3=4013
2n=4010
n=2005