20684857 has 4 divisors (see below), whose sum is σ = 20721780. Its totient is φ = 20647936.

The previous prime is 20684837. The next prime is 20684879. The reversal of 20684857 is 75848602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 75848602 = 2 ⋅37924301.

It can be written as a sum of positive squares in 2 ways, for example, as 4596736 + 16088121 = 2144^2 + 4011^2 .

It is a 4-Lehmer number, since φ(20684857) divides (20684857-1)⁴.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20684857 is a prime.

It is a super-2 number, since 2×20684857² = 855726618220898, 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 not an unprimeable number, because it can be changed into a prime (20684827) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17608 + ... + 18745.

It is an arithmetic number, because the mean of its divisors is an integer number (5180445).

Almost surely, 2^20684857 is an apocalyptic number.

It is an amenable number.

20684857 is a deficient number, since it is larger than the sum of its proper divisors (36923).

20684857 is an equidigital number, since it uses as much as digits as its factorization.

20684857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36922.

The product of its (nonzero) digits is 107520, while the sum is 40.

The square root of 20684857 is about 4548.0607955479. The cubic root of 20684857 is about 274.5053676056.

The spelling of 20684857 in words is "twenty million, six hundred eighty-four thousand, eight hundred fifty-seven".