21228904 has 8 divisors (see below), whose sum is σ = 39804210. Its totient is φ = 10614448.

The previous prime is 21228901. The next prime is 21228953. The reversal of 21228904 is 40982212.

It can be written as a sum of positive squares in only one way, i.e., 17656804 + 3572100 = 4202^2 + 1890^2 .

It is a tau number, because it is divible by the number of its divisors (8).

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

It is not an unprimeable number, because it can be changed into a prime (21228901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1326799 + ... + 1326814.

Almost surely, 2^21228904 is an apocalyptic number.

It is an amenable number.

21228904 is a deficient number, since it is larger than the sum of its proper divisors (18575306).

21228904 is a wasteful number, since it uses less digits than its factorization.

21228904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2653619 (or 2653615 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21228904 is about 4607.4834779953. The cubic root of 21228904 is about 276.8912239558.

It can be divided in two parts, 2122 and 8904, that added together give a triangular number (11026 = T₁₄₈).

The spelling of 21228904 in words is "twenty-one million, two hundred twenty-eight thousand, nine hundred four".