21808191 has 8 divisors (see below), whose sum is σ = 29157040. Its totient is φ = 14499072.

The previous prime is 21808177. The next prime is 21808217. The reversal of 21808191 is 19180812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21808191 - 2⁹ = 21807679 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21808121) 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 7 ways as a sum of consecutive naturals, for example, 8626 + ... + 10863.

It is an arithmetic number, because the mean of its divisors is an integer number (3644630).

Almost surely, 2^21808191 is an apocalyptic number.

21808191 is a deficient number, since it is larger than the sum of its proper divisors (7348849).

21808191 is a wasteful number, since it uses less digits than its factorization.

21808191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19865.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 21808191 is about 4669.9240893188. The cubic root of 21808191 is about 279.3872271173.

The spelling of 21808191 in words is "twenty-one million, eight hundred eight thousand, one hundred ninety-one".