21023021 has 4 divisors (see below), whose sum is σ = 21227232. Its totient is φ = 20818812.

The previous prime is 21023017. The next prime is 21023047. The reversal of 21023021 is 12032012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21023021 - 2² = 21023017 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21022993 and 21023011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21022021) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 101951 + ... + 102156.

It is an arithmetic number, because the mean of its divisors is an integer number (5306808).

Almost surely, 2^21023021 is an apocalyptic number.

It is an amenable number.

21023021 is a deficient number, since it is larger than the sum of its proper divisors (204211).

21023021 is a wasteful number, since it uses less digits than its factorization.

21023021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 204210.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21023021 is about 4585.0868039766. The cubic root of 21023021 is about 275.9931954144.

Adding to 21023021 its reverse (12032012), we get a palindrome (33055033).

The spelling of 21023021 in words is "twenty-one million, twenty-three thousand, twenty-one".