21205023 has 16 divisors (see below), whose sum is σ = 33355776. Its totient is φ = 11725920.

The previous prime is 21205021. The next prime is 21205027. The reversal of 21205023 is 32050212.

It is not a de Polignac number, because 21205023 - 2¹ = 21205021 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21204993 and 21205011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205021) 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 15 ways as a sum of consecutive naturals, for example, 15636 + ... + 16937.

It is an arithmetic number, because the mean of its divisors is an integer number (2084736).

Almost surely, 2^21205023 is an apocalyptic number.

21205023 is a deficient number, since it is larger than the sum of its proper divisors (12150753).

21205023 is a wasteful number, since it uses less digits than its factorization.

21205023 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32614.

The product of its (nonzero) digits is 120, while the sum is 15.

The square root of 21205023 is about 4604.8912039265. The cubic root of 21205023 is about 276.7873573850.

Adding to 21205023 its reverse (32050212), we get a palindrome (53255235).

The spelling of 21205023 in words is "twenty-one million, two hundred five thousand, twenty-three".