21205918 has 8 divisors (see below), whose sum is σ = 32330520. Its totient is φ = 10429080.

The previous prime is 21205913. The next prime is 21205927. The reversal of 21205918 is 81950212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205913) 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 3 ways as a sum of consecutive naturals, for example, 86788 + ... + 87031.

It is an arithmetic number, because the mean of its divisors is an integer number (4041315).

Almost surely, 2^21205918 is an apocalyptic number.

21205918 is a deficient number, since it is larger than the sum of its proper divisors (11124602).

21205918 is a wasteful number, since it uses less digits than its factorization.

21205918 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 173882.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 21205918 is about 4604.9883821786. The cubic root of 21205918 is about 276.7912514498.

The spelling of 21205918 in words is "twenty-one million, two hundred five thousand, nine hundred eighteen".