21011100021 has 24 divisors (see below), whose sum is σ = 30541242264. Its totient is φ = 13919109120.

The previous prime is 21011100017. The next prime is 21011100067. The reversal of 21011100021 is 12000111012.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 5904231921 + 15106868100 = 76839^2 + 122910^2 .

It is not a de Polignac number, because 21011100021 - 2² = 21011100017 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21011099976 and 21011100012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011100221) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 962985 + ... + 984561.

It is an arithmetic number, because the mean of its divisors is an integer number (1272551761).

Almost surely, 2^21011100021 is an apocalyptic number.

It is an amenable number.

21011100021 is a deficient number, since it is larger than the sum of its proper divisors (9530142243).

21011100021 is a wasteful number, since it uses less digits than its factorization.

21011100021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22261 (or 22258 counting only the distinct ones).

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

Adding to 21011100021 its reverse (12000111012), we get a palindrome (33011211033).

The spelling of 21011100021 in words is "twenty-one billion, eleven million, one hundred thousand, twenty-one".