21204431 has 4 divisors (see below), whose sum is σ = 21246600. Its totient is φ = 21162264.

The previous prime is 21204419. The next prime is 21204451. The reversal of 21204431 is 13440212.

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 21204431 - 2¹⁰ = 21203407 is a prime.

It is a super-2 number, since 2×21204431² = 899255788067522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21204451) 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, 20321 + ... + 21338.

It is an arithmetic number, because the mean of its divisors is an integer number (5311650).

Almost surely, 2^21204431 is an apocalyptic number.

21204431 is a deficient number, since it is larger than the sum of its proper divisors (42169).

21204431 is an equidigital number, since it uses as much as digits as its factorization.

21204431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42168.

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21204431 is about 4604.8269240005. The cubic root of 21204431 is about 276.7847815859.

Adding to 21204431 its reverse (13440212), we get a palindrome (34644643).

The spelling of 21204431 in words is "twenty-one million, two hundred four thousand, four hundred thirty-one".