Let be a positive integer. A number consists of digits, each of which is ; and a number consists of digits, each of which is . Prove that is a perfect square.
Let $n$ be a positive integer. A number $A$ consists of $2n$ digits, each of which is $4$; and a number $B$ consists of $n$ digits, each of which is $8$. Prove that $A+2B+4$ is a perfect square.
Školjka 
be a positive integer. A number 
consists of 
digits, each of which is 
; and a number 
consists of 
. Prove that 
is a perfect square.