21500521 has 4 divisors (see below), whose sum is σ = 24572032. Its totient is φ = 18429012.

The previous prime is 21500519. The next prime is 21500527. The reversal of 21500521 is 12500512.

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 not a de Polignac number, because 21500521 - 2¹ = 21500519 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21500495 and 21500504.

It is not an unprimeable number, because it can be changed into a prime (21500527) 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, 1535745 + ... + 1535758.

It is an arithmetic number, because the mean of its divisors is an integer number (6143008).

Almost surely, 2^21500521 is an apocalyptic number.

It is an amenable number.

21500521 is a deficient number, since it is larger than the sum of its proper divisors (3071511).

21500521 is an equidigital number, since it uses as much as digits as its factorization.

21500521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3071510.

The product of its (nonzero) digits is 100, while the sum is 16.

The square root of 21500521 is about 4636.8654282823. The cubic root of 21500521 is about 278.0671343824.

Subtracting from 21500521 its reverse (12500512), we obtain a palindrome (9000009).

The spelling of 21500521 in words is "twenty-one million, five hundred thousand, five hundred twenty-one".