21624521 has 4 divisors (see below), whose sum is σ = 21637392. Its totient is φ = 21611652.

The previous prime is 21624509. The next prime is 21624529. The reversal of 21624521 is 12542612.

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 a de Polignac number, because none of the positive numbers 2^k-21624521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21624529) 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, 3455 + ... + 7428.

It is an arithmetic number, because the mean of its divisors is an integer number (5409348).

Almost surely, 2^21624521 is an apocalyptic number.

It is an amenable number.

21624521 is a deficient number, since it is larger than the sum of its proper divisors (12871).

21624521 is a wasteful number, since it uses less digits than its factorization.

21624521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12870.

The product of its digits is 960, while the sum is 23.

The square root of 21624521 is about 4650.2173067503. The cubic root of 21624521 is about 278.6006757183.

The spelling of 21624521 in words is "twenty-one million, six hundred twenty-four thousand, five hundred twenty-one".