FIND SQUARE OF ANY NUMBER IN A 1 STEP

Find Square from Sum of n numbers

n² = (Sum of 'n' numbers * 2) - n


Example 

If, n=5
5² = (15 * 2) - 5 = 30 - 5 = 25

Note: 
Sum of 'n' numbers = [n*(n+1)] / 2

source:hiox