21120021 has 40 divisors (see below), whose sum is σ = 35126784. Its totient is φ = 12558240.

The previous prime is 21120019. The next prime is 21120041. The reversal of 21120021 is 12002112.

It is not a de Polignac number, because 21120021 - 2¹ = 21120019 is a prime.

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

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21119985 and 21120012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21120041) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 32320 + ... + 32966.

Almost surely, 2^21120021 is an apocalyptic number.

It is an amenable number.

21120021 is a deficient number, since it is larger than the sum of its proper divisors (14006763).

21120021 is a wasteful number, since it uses less digits than its factorization.

21120021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 703 (or 694 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21120021 is about 4595.6524019991. The cubic root of 21120021 is about 276.4170208159.

Adding to 21120021 its reverse (12002112), we get a palindrome (33122133).

The spelling of 21120021 in words is "twenty-one million, one hundred twenty thousand, twenty-one".