206815891 has 4 divisors (see below), whose sum is σ = 206892784. Its totient is φ = 206739000.

The previous prime is 206815883. The next prime is 206815909. The reversal of 206815891 is 198518602.

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 206815891 - 2³ = 206815883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (206815811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 34260 + ... + 39841.

It is an arithmetic number, because the mean of its divisors is an integer number (51723196).

Almost surely, 2^206815891 is an apocalyptic number.

206815891 is a deficient number, since it is larger than the sum of its proper divisors (76893).

206815891 is an equidigital number, since it uses as much as digits as its factorization.

206815891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76892.

The product of its (nonzero) digits is 34560, while the sum is 40.

The square root of 206815891 is about 14381.0949165910. The cubic root of 206815891 is about 591.3727405876.

The spelling of 206815891 in words is "two hundred six million, eight hundred fifteen thousand, eight hundred ninety-one".