20640689 has 4 divisors (see below), whose sum is σ = 20889456. Its totient is φ = 20391924.

The previous prime is 20640679. The next prime is 20640713. The reversal of 20640689 is 98604602.

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.

It is a cyclic number.

It is not a de Polignac number, because 20640689 - 2²⁴ = 3863473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20640679) 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, 124259 + ... + 124424.

It is an arithmetic number, because the mean of its divisors is an integer number (5222364).

Almost surely, 2^20640689 is an apocalyptic number.

It is an amenable number.

20640689 is a deficient number, since it is larger than the sum of its proper divisors (248767).

20640689 is an equidigital number, since it uses as much as digits as its factorization.

20640689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 248766.

The product of its (nonzero) digits is 20736, while the sum is 35.

The square root of 20640689 is about 4543.2025048417. The cubic root of 20640689 is about 274.3098462642.

The spelling of 20640689 in words is "twenty million, six hundred forty thousand, six hundred eighty-nine".