21561923 has 4 divisors (see below), whose sum is σ = 21589008. Its totient is φ = 21534840.

The previous prime is 21561893. The next prime is 21561929. The reversal of 21561923 is 32916512.

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 21561923 - 2²² = 17367619 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21561929) 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, 12311 + ... + 13952.

It is an arithmetic number, because the mean of its divisors is an integer number (5397252).

Almost surely, 2^21561923 is an apocalyptic number.

21561923 is a deficient number, since it is larger than the sum of its proper divisors (27085).

21561923 is an equidigital number, since it uses as much as digits as its factorization.

21561923 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27084.

The product of its digits is 3240, while the sum is 29.

The square root of 21561923 is about 4643.4817755645. The cubic root of 21561923 is about 278.3315876720.

The spelling of 21561923 in words is "twenty-one million, five hundred sixty-one thousand, nine hundred twenty-three".