21657428 has 24 divisors (see below), whose sum is σ = 41201160. Its totient is φ = 9901440.

The previous prime is 21657407. The next prime is 21657431. The reversal of 21657428 is 82475612.

It can be written as a sum of positive squares in 4 ways, for example, as 5513104 + 16144324 = 2348^2 + 4018^2 .

It is a congruent number.

It is an unprimeable number.

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 in 7 ways as a sum of consecutive naturals, for example, 3758 + ... + 7578.

It is an arithmetic number, because the mean of its divisors is an integer number (1716715).

Almost surely, 2^21657428 is an apocalyptic number.

It is an amenable number.

21657428 is a deficient number, since it is larger than the sum of its proper divisors (19543732).

21657428 is a wasteful number, since it uses less digits than its factorization.

21657428 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3947 (or 3945 counting only the distinct ones).

The product of its digits is 26880, while the sum is 35.

The square root of 21657428 is about 4653.7541834523. The cubic root of 21657428 is about 278.7419237942.

The spelling of 21657428 in words is "twenty-one million, six hundred fifty-seven thousand, four hundred twenty-eight".