1+3+5+...+(2n-1) = sum^{n}_{i=1} (2n-1) = 2n(1+n)/2 - n = n^2 + n - n = n^2
ex: 1 + 3 + 5 + 7 + 9
9 = (2n-1) , n = 5
1 + 3 + 5 + 7 + 9 = 5^2 = 25