20840857 has 4 divisors (see below), whose sum is σ = 20854836. Its totient is φ = 20826880.

The previous prime is 20840839. The next prime is 20840873. The reversal of 20840857 is 75804802.

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

It can be written as a sum of positive squares in 2 ways, for example, as 19263321 + 1577536 = 4389^2 + 1256^2 .

It is a cyclic number.

It is not a de Polignac number, because 20840857 - 2²³ = 12452249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20840837) by changing a digit.

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 in 3 ways as a sum of consecutive naturals, for example, 4444 + ... + 7837.

It is an arithmetic number, because the mean of its divisors is an integer number (5213709).

Almost surely, 2^20840857 is an apocalyptic number.

It is an amenable number.

20840857 is a deficient number, since it is larger than the sum of its proper divisors (13979).

20840857 is a wasteful number, since it uses less digits than its factorization.

20840857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13978.

The product of its (nonzero) digits is 17920, while the sum is 34.

The square root of 20840857 is about 4565.1787478696. The cubic root of 20840857 is about 275.1937235546.

The spelling of 20840857 in words is "twenty million, eight hundred forty thousand, eight hundred fifty-seven".