21440728 has 8 divisors (see below), whose sum is σ = 40201380. Its totient is φ = 10720360.

The previous prime is 21440719. The next prime is 21440801. The reversal of 21440728 is 82704412.

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 a junction number, because it is equal to n+sod(n) for n = 21440696 and 21440705.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1340038 + ... + 1340053.

Almost surely, 2^21440728 is an apocalyptic number.

It is an amenable number.

21440728 is a deficient number, since it is larger than the sum of its proper divisors (18760652).

21440728 is a wasteful number, since it uses less digits than its factorization.

21440728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2680097 (or 2680093 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21440728 is about 4630.4133724755. The cubic root of 21440728 is about 277.8091266072.

The spelling of 21440728 in words is "twenty-one million, four hundred forty thousand, seven hundred twenty-eight".