21010021 has 4 divisors (see below), whose sum is σ = 21019552. Its totient is φ = 21000492.

The previous prime is 21010013. The next prime is 21010037. The reversal of 21010021 is 12001012.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21010021 - 2³ = 21010013 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21009986 and 21010013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21010321) 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, 430 + ... + 6496.

It is an arithmetic number, because the mean of its divisors is an integer number (5254888).

Almost surely, 2^21010021 is an apocalyptic number.

It is an amenable number.

21010021 is a deficient number, since it is larger than the sum of its proper divisors (9531).

21010021 is an equidigital number, since it uses as much as digits as its factorization.

21010021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9530.

The product of its (nonzero) digits is 4, while the sum is 7.

The square root of 21010021 is about 4583.6689452883. The cubic root of 21010021 is about 275.9362950709.

Adding to 21010021 its reverse (12001012), we get a palindrome (33011033).

Subtracting from 21010021 its reverse (12001012), we obtain a palindrome (9009009).

The spelling of 21010021 in words is "twenty-one million, ten thousand, twenty-one".