21209885 has 4 divisors (see below), whose sum is σ = 25451868. Its totient is φ = 16967904.

The previous prime is 21209873. The next prime is 21209927. The reversal of 21209885 is 58890212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 5257849 + 15952036 = 2293^2 + 3994^2 .

It is a cyclic number.

It is not a de Polignac number, because 21209885 - 2⁴ = 21209869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120984 + ... + 2120993.

It is an arithmetic number, because the mean of its divisors is an integer number (6362967).

Almost surely, 2^21209885 is an apocalyptic number.

It is an amenable number.

21209885 is a deficient number, since it is larger than the sum of its proper divisors (4241983).

21209885 is an equidigital number, since it uses as much as digits as its factorization.

21209885 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241982.

The product of its (nonzero) digits is 11520, while the sum is 35.

The square root of 21209885 is about 4605.4190905932. The cubic root of 21209885 is about 276.8085101923.

The spelling of 21209885 in words is "twenty-one million, two hundred nine thousand, eight hundred eighty-five".