21204423 has 56 divisors (see below), whose sum is σ = 35413200. Its totient is φ = 12628224.

The previous prime is 21204419. The next prime is 21204451. The reversal of 21204423 is 32440212.

It is not a de Polignac number, because 21204423 - 2² = 21204419 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21204396 and 21204405.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21204493) 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 55 ways as a sum of consecutive naturals, for example, 359368 + ... + 359426.

Almost surely, 2^21204423 is an apocalyptic number.

21204423 is a deficient number, since it is larger than the sum of its proper divisors (14208777).

21204423 is an equidigital number, since it uses as much as digits as its factorization.

21204423 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123 (or 108 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 21204423 is about 4604.8260553467. The cubic root of 21204423 is about 276.7847467775.

Adding to 21204423 its reverse (32440212), we get a palindrome (53644635).

The spelling of 21204423 in words is "twenty-one million, two hundred four thousand, four hundred twenty-three".