21091111 has 4 divisors (see below), whose sum is σ = 21277872. Its totient is φ = 20904352.

The previous prime is 21091079. The next prime is 21091139. The reversal of 21091111 is 11119012.

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 21091111 - 2⁵ = 21091079 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 (21091151) 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, 93211 + ... + 93436.

It is an arithmetic number, because the mean of its divisors is an integer number (5319468).

Almost surely, 2^21091111 is an apocalyptic number.

21091111 is a deficient number, since it is larger than the sum of its proper divisors (186761).

21091111 is a wasteful number, since it uses less digits than its factorization.

21091111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186760.

The product of its (nonzero) digits is 18, while the sum is 16.

The square root of 21091111 is about 4592.5059608018. The cubic root of 21091111 is about 276.2908393585.

The spelling of 21091111 in words is "twenty-one million, ninety-one thousand, one hundred eleven".