21204243 has 12 divisors (see below), whose sum is σ = 30932928. Its totient is φ = 13995600.

The previous prime is 21204241. The next prime is 21204251. The reversal of 21204243 is 34240212.

It is not a de Polignac number, because 21204243 - 2¹ = 21204241 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21204241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10755 + ... + 12572.

It is an arithmetic number, because the mean of its divisors is an integer number (2577744).

Almost surely, 2^21204243 is an apocalyptic number.

21204243 is a deficient number, since it is larger than the sum of its proper divisors (9728685).

21204243 is a wasteful number, since it uses less digits than its factorization.

21204243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23434 (or 23431 counting only the distinct ones).

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

The square root of 21204243 is about 4604.8065105930. The cubic root of 21204243 is about 276.7839635856.

Adding to 21204243 its reverse (34240212), we get a palindrome (55444455).

The spelling of 21204243 in words is "twenty-one million, two hundred four thousand, two hundred forty-three".