21630823 has 4 divisors (see below), whose sum is σ = 21654160. Its totient is φ = 21607488.

The previous prime is 21630779. The next prime is 21630841. The reversal of 21630823 is 32803612.

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 21630823 - 2¹³ = 21622631 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 (21630853) 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 3 ways as a sum of consecutive naturals, for example, 10218 + ... + 12151.

It is an arithmetic number, because the mean of its divisors is an integer number (5413540).

Almost surely, 2^21630823 is an apocalyptic number.

21630823 is a deficient number, since it is larger than the sum of its proper divisors (23337).

21630823 is an equidigital number, since it uses as much as digits as its factorization.

21630823 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23336.

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21630823 is about 4650.8948601318. The cubic root of 21630823 is about 278.6277371412.

The spelling of 21630823 in words is "twenty-one million, six hundred thirty thousand, eight hundred twenty-three".