20808257 has 4 divisors (see below), whose sum is σ = 21118896. Its totient is φ = 20497620.

The previous prime is 20808251. The next prime is 20808301. The reversal of 20808257 is 75280802.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 75280802 = 2 ⋅37640401.

It is a cyclic number.

It is not a de Polignac number, because 20808257 - 2⁴ = 20808241 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20808251) 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, 155219 + ... + 155352.

It is an arithmetic number, because the mean of its divisors is an integer number (5279724).

Almost surely, 2^20808257 is an apocalyptic number.

It is an amenable number.

20808257 is a deficient number, since it is larger than the sum of its proper divisors (310639).

20808257 is an equidigital number, since it uses as much as digits as its factorization.

20808257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 310638.

The product of its (nonzero) digits is 8960, while the sum is 32.

The square root of 20808257 is about 4561.6068440847. The cubic root of 20808257 is about 275.0501594455.

The spelling of 20808257 in words is "twenty million, eight hundred eight thousand, two hundred fifty-seven".