Square numbers: 1,4,9,16,…1, 4, 9, 16, \ldots1,4,9,16,…. Sum of first nnn odd numbers =n2= n^2=n2. (n+1)2−n2=2n+1(n+1)^2 - n^2 = 2n+1(n+1)2−n2=2n+1.