21156023 has 4 divisors (see below), whose sum is σ = 24178320. Its totient is φ = 18133728.

The previous prime is 21156019. The next prime is 21156029. The reversal of 21156023 is 32065112.

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 21156023 - 2² = 21156019 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21155986 and 21156004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21156029) 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, 1511138 + ... + 1511151.

It is an arithmetic number, because the mean of its divisors is an integer number (6044580).

Almost surely, 2^21156023 is an apocalyptic number.

21156023 is a deficient number, since it is larger than the sum of its proper divisors (3022297).

21156023 is an equidigital number, since it uses as much as digits as its factorization.

21156023 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3022296.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21156023 is about 4599.5676970776. The cubic root of 21156023 is about 276.5739953493.

The spelling of 21156023 in words is "twenty-one million, one hundred fifty-six thousand, twenty-three".