21172828 has 6 divisors (see below), whose sum is σ = 37052456. Its totient is φ = 10586412.

The previous prime is 21172819. The next prime is 21172829. The reversal of 21172828 is 82827112.

It is a self number, because there is not a number n which added to its sum of digits gives 21172828.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172829) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2646600 + ... + 2646607.

Almost surely, 2^21172828 is an apocalyptic number.

It is an amenable number.

21172828 is a deficient number, since it is larger than the sum of its proper divisors (15879628).

21172828 is a wasteful number, since it uses less digits than its factorization.

21172828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5293211 (or 5293209 counting only the distinct ones).

The product of its digits is 3584, while the sum is 31.

The square root of 21172828 is about 4601.3941365634. The cubic root of 21172828 is about 276.6472069021.

The spelling of 21172828 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred twenty-eight".