21530207 has 4 divisors (see below), whose sum is σ = 22055376. Its totient is φ = 21005040.

The previous prime is 21530161. The next prime is 21530227. The reversal of 21530207 is 70203512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21530207 - 2¹⁶ = 21464671 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21530227) 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, 262523 + ... + 262604.

It is an arithmetic number, because the mean of its divisors is an integer number (5513844).

Almost surely, 2^21530207 is an apocalyptic number.

21530207 is a deficient number, since it is larger than the sum of its proper divisors (525169).

21530207 is an equidigital number, since it uses as much as digits as its factorization.

21530207 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 525168.

The product of its (nonzero) digits is 420, while the sum is 20.

The square root of 21530207 is about 4640.0654090217. The cubic root of 21530207 is about 278.1950522865.

Adding to 21530207 its reverse (70203512), we get a palindrome (91733719).

The spelling of 21530207 in words is "twenty-one million, five hundred thirty thousand, two hundred seven".