21530021 has 4 divisors (see below), whose sum is σ = 22663200. Its totient is φ = 20396844.

The previous prime is 21530017. The next prime is 21530077. The reversal of 21530021 is 12003512.

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 21530021 - 2² = 21530017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21529978 and 21530005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21530321) 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, 566561 + ... + 566598.

It is an arithmetic number, because the mean of its divisors is an integer number (5665800).

Almost surely, 2^21530021 is an apocalyptic number.

It is an amenable number.

21530021 is a deficient number, since it is larger than the sum of its proper divisors (1133179).

21530021 is a wasteful number, since it uses less digits than its factorization.

21530021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1133178.

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21530021 is about 4640.0453661575. The cubic root of 21530021 is about 278.1942511728.

Adding to 21530021 its reverse (12003512), we get a palindrome (33533533).

The spelling of 21530021 in words is "twenty-one million, five hundred thirty thousand, twenty-one".