21084821 has 4 divisors (see below), whose sum is σ = 21289632. Its totient is φ = 20880012.

The previous prime is 21084803. The next prime is 21084829. The reversal of 21084821 is 12848012.

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 21084821 - 2¹⁸ = 20822677 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21084829) 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, 102251 + ... + 102456.

It is an arithmetic number, because the mean of its divisors is an integer number (5322408).

Almost surely, 2^21084821 is an apocalyptic number.

It is an amenable number.

21084821 is a deficient number, since it is larger than the sum of its proper divisors (204811).

21084821 is a wasteful number, since it uses less digits than its factorization.

21084821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 204810.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 21084821 is about 4591.8210984314. The cubic root of 21084821 is about 276.2633705642.

The spelling of 21084821 in words is "twenty-one million, eighty-four thousand, eight hundred twenty-one".