20857639 has 4 divisors (see below), whose sum is σ = 22753800. Its totient is φ = 18961480.

The previous prime is 20857631. The next prime is 20857663. The reversal of 20857639 is 93675802.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20857639 - 2³ = 20857631 is a prime.

It is a super-2 number, since 2×20857639² = 870082209308642, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20857631) 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 in 3 ways as a sum of consecutive naturals, for example, 948064 + ... + 948085.

It is an arithmetic number, because the mean of its divisors is an integer number (5688450).

Almost surely, 2^20857639 is an apocalyptic number.

20857639 is a deficient number, since it is larger than the sum of its proper divisors (1896161).

20857639 is a wasteful number, since it uses less digits than its factorization.

20857639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1896160.

The product of its (nonzero) digits is 90720, while the sum is 40.

The square root of 20857639 is about 4567.0164221294. The cubic root of 20857639 is about 275.2675698781.

The spelling of 20857639 in words is "twenty million, eight hundred fifty-seven thousand, six hundred thirty-nine".