Pretty simple stuff
Here's the equation:
a^2=b+c where b is the the previous answer and c is the next odd number.
i.e. 4^2=16 or 4^2=9+7 because 3^2=9 so b=9 and c=7 because its the 4th odd number.
In other words to find c just take the number you're squaring and add the correct ending like for 10^2 take 10 and make it Tenth then count out 10 odd numbers 1,3,5,7,9,11,13,15,17,19. So 10^2=9^2+19
Or use a handy dandy caculator lol
