21205013 has 4 divisors (see below), whose sum is σ = 21564480. Its totient is φ = 20845548.

The previous prime is 21204949. The next prime is 21205021. The reversal of 21205013 is 31050212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21205013 - 2⁶ = 21204949 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 (21205043) 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, 179645 + ... + 179762.

It is an arithmetic number, because the mean of its divisors is an integer number (5391120).

Almost surely, 2^21205013 is an apocalyptic number.

It is an amenable number.

21205013 is a deficient number, since it is larger than the sum of its proper divisors (359467).

21205013 is an equidigital number, since it uses as much as digits as its factorization.

21205013 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 359466.

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21205013 is about 4604.8901181244. The cubic root of 21205013 is about 276.7873138753.

Adding to 21205013 its reverse (31050212), we get a palindrome (52255225).

The spelling of 21205013 in words is "twenty-one million, two hundred five thousand, thirteen".