21868521 has 4 divisors (see below), whose sum is σ = 29158032. Its totient is φ = 14579012.

The previous prime is 21868519. The next prime is 21868529. The reversal of 21868521 is 12586812.

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 21868521 - 2¹ = 21868519 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21868529) 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, 3644751 + ... + 3644756.

It is an arithmetic number, because the mean of its divisors is an integer number (7289508).

Almost surely, 2^21868521 is an apocalyptic number.

It is an amenable number.

21868521 is a deficient number, since it is larger than the sum of its proper divisors (7289511).

21868521 is an equidigital number, since it uses as much as digits as its factorization.

21868521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7289510.

The product of its digits is 7680, while the sum is 33.

The square root of 21868521 is about 4676.3790479387. The cubic root of 21868521 is about 279.6446214200.

The spelling of 21868521 in words is "twenty-one million, eight hundred sixty-eight thousand, five hundred twenty-one".