21000010021 has 4 divisors (see below), whose sum is σ = 21125758752. Its totient is φ = 20874261292.

The previous prime is 21000010001. The next prime is 21000010037. The reversal of 21000010021 is 12001000012.

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 21000010021 - 2⁷ = 21000009893 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21000009986 and 21000010013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000010001) 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, 62874115 + ... + 62874448.

It is an arithmetic number, because the mean of its divisors is an integer number (5281439688).

Almost surely, 2^21000010021 is an apocalyptic number.

It is an amenable number.

21000010021 is a deficient number, since it is larger than the sum of its proper divisors (125748731).

21000010021 is a wasteful number, since it uses less digits than its factorization.

21000010021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125748730.

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

Adding to 21000010021 its reverse (12001000012), we get a palindrome (33001010033).

The spelling of 21000010021 in words is "twenty-one billion, ten thousand, twenty-one".