21011010021 has 6 divisors (see below), whose sum is σ = 30349236710. Its totient is φ = 14007340008.

The previous prime is 21011010011. The next prime is 21011010029. The reversal of 21011010021 is 12001011012.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 21004704900 + 6305121 = 144930^2 + 2511^2 .

It is not a de Polignac number, because 21011010021 - 2⁷ = 21011009893 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2334556669 = 21011010021 / (2 + 1 + 0 + 1 + 1 + 0 + 1 + 0 + 0 + 2 + 1).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21011009985 and 21011010012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011010029) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1167278326 + ... + 1167278343.

Almost surely, 2^21011010021 is an apocalyptic number.

It is an amenable number.

21011010021 is a deficient number, since it is larger than the sum of its proper divisors (9338226689).

21011010021 is a wasteful number, since it uses less digits than its factorization.

21011010021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2334556675 (or 2334556672 counting only the distinct ones).

The product of its (nonzero) digits is 4, while the sum is 9.

Adding to 21011010021 its reverse (12001011012), we get a palindrome (33012021033).

Subtracting from 21011010021 its reverse (12001011012), we obtain a palindrome (9009999009).

The spelling of 21011010021 in words is "twenty-one billion, eleven million, ten thousand, twenty-one".