2n(2n+2)+1=(2n+1)²证明：2n(2n+2)+1=4n²+2*2n+1=(2n+1)²
n*(n+2)+1=n^2+2n+1=(n+1)^2
(n-1)*(n+1)+1=n^2
(3n-1)×(3n+1)+1=(3n)^2
