21110021 has 4 divisors (see below), whose sum is σ = 22027872. Its totient is φ = 20192172.

The previous prime is 21109987. The next prime is 21110027. The reversal of 21110021 is 12001112.

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 21110021 - 2¹⁸ = 20847877 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21109990 and 21110008.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21110027) 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, 458891 + ... + 458936.

It is an arithmetic number, because the mean of its divisors is an integer number (5506968).

Almost surely, 2^21110021 is an apocalyptic number.

It is an amenable number.

21110021 is a deficient number, since it is larger than the sum of its proper divisors (917851).

21110021 is an equidigital number, since it uses as much as digits as its factorization.

21110021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 917850.

The product of its (nonzero) digits is 4, while the sum is 8.

The square root of 21110021 is about 4594.5642883738. The cubic root of 21110021 is about 276.3733875482.

Adding to 21110021 its reverse (12001112), we get a palindrome (33111133).

The spelling of 21110021 in words is "twenty-one million, one hundred ten thousand, twenty-one".