21011021 has 8 divisors (see below), whose sum is σ = 21824640. Its totient is φ = 20212768.

The previous prime is 21011009. The next prime is 21011033. The reversal of 21011021 is 12011012.

It is an interprime number because it is at equal distance from previous prime (21011009) and next prime (21011033).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21011021 - 2¹⁰ = 21009997 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011071) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1016 + ... + 6561.

It is an arithmetic number, because the mean of its divisors is an integer number (2728080).

Almost surely, 2^21011021 is an apocalyptic number.

It is an amenable number.

21011021 is a deficient number, since it is larger than the sum of its proper divisors (813619).

21011021 is an equidigital number, since it uses as much as digits as its factorization.

21011021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7683.

The product of its (nonzero) digits is 4, while the sum is 8.

The square root of 21011021 is about 4583.7780269119. The cubic root of 21011021 is about 275.9406728536.

Adding to 21011021 its reverse (12011012), we get a palindrome (33022033).

Subtracting from 21011021 its reverse (12011012), we obtain a palindrome (9000009).

The spelling of 21011021 in words is "twenty-one million, eleven thousand, twenty-one".