21891913 has 4 divisors (see below), whose sum is σ = 21915520. Its totient is φ = 21868308.

The previous prime is 21891911. The next prime is 21891931. The reversal of 21891913 is 31919812.

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 21891913 - 2¹ = 21891911 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10353 + ... + 12286.

It is an arithmetic number, because the mean of its divisors is an integer number (5478880).

Almost surely, 2^21891913 is an apocalyptic number.

It is an amenable number.

21891913 is a deficient number, since it is larger than the sum of its proper divisors (23607).

21891913 is an equidigital number, since it uses as much as digits as its factorization.

21891913 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23606.

The product of its digits is 3888, while the sum is 34.

The square root of 21891913 is about 4678.8794598707. The cubic root of 21891913 is about 279.7442946136.

The spelling of 21891913 in words is "twenty-one million, eight hundred ninety-one thousand, nine hundred thirteen".