20391689 has 4 divisors (see below), whose sum is σ = 20637456. Its totient is φ = 20145924.

The previous prime is 20391677. The next prime is 20391713. The reversal of 20391689 is 98619302.

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 20391689 - 2⁸ = 20391433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20391289) 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, 122759 + ... + 122924.

It is an arithmetic number, because the mean of its divisors is an integer number (5159364).

Almost surely, 2^20391689 is an apocalyptic number.

It is an amenable number.

20391689 is a deficient number, since it is larger than the sum of its proper divisors (245767).

20391689 is an equidigital number, since it uses as much as digits as its factorization.

20391689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 245766.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 20391689 is about 4515.7157793643. The cubic root of 20391689 is about 273.2023304745.

The spelling of 20391689 in words is "twenty million, three hundred ninety-one thousand, six hundred eighty-nine".