16-1=15 => 4^2-1^1=(4+1)(4-1)
25-4=21,=> 5^2-2^2=(5+2)(5-2)
36-9=27,=> 6^2-3^2=(6+3)(6-3)
49-16=33 => 7^2-4^2=(7+4)(7-4)
用带N的式子表示他的规律
(n+3)^2-n^2=[(n+3)+n][(n+3)-n]=3*(2n+3)=6n+9