20643691 has 4 divisors (see below), whose sum is σ = 20675584. Its totient is φ = 20611800.

The previous prime is 20643683. The next prime is 20643697. The reversal of 20643691 is 19634602.

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

It is a cyclic number.

It is not a de Polignac number, because 20643691 - 2³ = 20643683 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20643697) 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, 14955 + ... + 16276.

It is an arithmetic number, because the mean of its divisors is an integer number (5168896).

Almost surely, 2^20643691 is an apocalyptic number.

20643691 is a deficient number, since it is larger than the sum of its proper divisors (31893).

20643691 is an equidigital number, since it uses as much as digits as its factorization.

20643691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31892.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 20643691 is about 4543.5328765180. The cubic root of 20643691 is about 274.3231442414.

The spelling of 20643691 in words is "twenty million, six hundred forty-three thousand, six hundred ninety-one".