The left side of this identity describes a square number, while the right side describes a triangular number, so the result is a square triangular number.
It is a square number (33 squared), a nonagonal number, a 32-gonal number, a 364-gonal number, and a centered octagonal number. 1089 is the first reverse-divisible number.
Another property of a square number is that it has an odd number of positive divisors, while other natural numbers have an even number of positive divisors.