$\text{I.}{11}^2-1=\left(5\cdot 6\right)\cdot 4$  

${17}^2-1=\left(8\cdot 9\right)\cdot 4$  

${13}^2-1=\left(8\cdot 7\right)\cdot 4$  

${25}^2-1=\left(12\cdot 13\right)\cdot 4$  

$\text{II.}{\left(2n+1\right)}^2=\left[\left(n+1\right)\cdot n\right]\cdot 4$