209728 has 28 divisors (see below), whose sum is σ = 434340. Its totient is φ = 100352.

The previous prime is 209719. The next prime is 209743. The reversal of 209728 is 827902.

209728 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 43264 + 166464 = 208^2 + 408^2 .

It is a Smith number, since the sum of its digits (28) coincides with the sum of the digits of its prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 209696 and 209705.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1800 + ... + 1912.

2²⁰⁹⁷²⁸ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 209728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (217170).

209728 is an abundant number, since it is smaller than the sum of its proper divisors (224612).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

209728 is a wasteful number, since it uses less digits than its factorization.

209728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 154 (or 144 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 209728 is about 457.9606970036. The cubic root of 209728 is about 59.4135457927.

The spelling of 209728 in words is "two hundred nine thousand, seven hundred twenty-eight".