21111021 has 6 divisors (see below), whose sum is σ = 30493710. Its totient is φ = 14074008.

The previous prime is 21111007. The next prime is 21111029. The reversal of 21111021 is 12011112.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 11655396 + 9455625 = 3414^2 + 3075^2 .

It is not a de Polignac number, because 21111021 - 2⁵ = 21110989 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: 2345669 = 21111021 / (2 + 1 + 1 + 1 + 1 + 0 + 2 + 1).

It is a junction number, because it is equal to n+sod(n) for n = 21110994 and 21111012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21111029) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1172826 + ... + 1172843.

It is an arithmetic number, because the mean of its divisors is an integer number (5082285).

Almost surely, 2^21111021 is an apocalyptic number.

It is an amenable number.

21111021 is a deficient number, since it is larger than the sum of its proper divisors (9382689).

21111021 is a wasteful number, since it uses less digits than its factorization.

21111021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2345675 (or 2345672 counting only the distinct ones).

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

The square root of 21111021 is about 4594.6731113323. The cubic root of 21111021 is about 276.3777514950.

Adding to 21111021 its reverse (12011112), we get a palindrome (33122133).

Subtracting from 21111021 its reverse (12011112), we obtain a palindrome (9099909).

The spelling of 21111021 in words is "twenty-one million, one hundred eleven thousand, twenty-one".