NOTE: This trick is valid for the numbers between 10 to 20
Let's take : 16
First of all multiply the unti place digit with same digit to get the PART TWO or last two digit of the desired Square that is "6" so :
6 * 6 = 36.
if value is two digit number then PART TWO of the result will be last digit that is 6 and carry will be 3
Now, we will add the unit place digit with the number and also add the carry if we have any.
16 + 6 + 3 = 25
So 162 = 256