21055021 has 8 divisors (see below), whose sum is σ = 23868320. Its totient is φ = 18412272.

The previous prime is 21055003. The next prime is 21055033. The reversal of 21055021 is 12055012.

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

It is a cyclic number.

It is not a de Polignac number, because 21055021 - 2⁷ = 21054893 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21054986 and 21055004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21055921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 42375 + ... + 42868.

It is an arithmetic number, because the mean of its divisors is an integer number (2983540).

Almost surely, 2^21055021 is an apocalyptic number.

It is an amenable number.

21055021 is a deficient number, since it is larger than the sum of its proper divisors (2813299).

21055021 is a wasteful number, since it uses less digits than its factorization.

21055021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85275.

The product of its (nonzero) digits is 100, while the sum is 16.

The square root of 21055021 is about 4588.5750511461. The cubic root of 21055021 is about 276.1331579340.

Subtracting from 21055021 its reverse (12055012), we obtain a palindrome (9000009).

The spelling of 21055021 in words is "twenty-one million, fifty-five thousand, twenty-one".