7×8×9×10+1=(7^2+3×7+1)^2，n(n+1)(n+2)(n+3)+1=[n^2+3n+1]^2.左边=[n(n+3)][(n+1)(n+2)]+1=(n^2+3n)(n^2+3n+2]+1=(n^2+3n)^2+2(n^2+3n)+1=(n^2+3n+1)^2=右边。
