21389855 has 4 divisors (see below), whose sum is σ = 25667832. Its totient is φ = 17111880.

The previous prime is 21389843. The next prime is 21389857. The reversal of 21389855 is 55898312.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21389855 - 2¹⁰ = 21388831 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 (21389857) 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, 2138981 + ... + 2138990.

It is an arithmetic number, because the mean of its divisors is an integer number (6416958).

Almost surely, 2^21389855 is an apocalyptic number.

21389855 is a deficient number, since it is larger than the sum of its proper divisors (4277977).

21389855 is an equidigital number, since it uses as much as digits as its factorization.

21389855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4277976.

The product of its digits is 86400, while the sum is 41.

The square root of 21389855 is about 4624.9167560076. The cubic root of 21389855 is about 277.5892308343.

The spelling of 21389855 in words is "twenty-one million, three hundred eighty-nine thousand, eight hundred fifty-five".