21644872 has 16 divisors (see below), whose sum is σ = 40679100. Its totient is φ = 10797120.

The previous prime is 21644849. The next prime is 21644879. The reversal of 21644872 is 27844612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 19412836 + 2232036 = 4406^2 + 1494^2 .

It is not an unprimeable number, because it can be changed into a prime (21644879) 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, 754 + ... + 6622.

Almost surely, 2^21644872 is an apocalyptic number.

It is an amenable number.

21644872 is a deficient number, since it is larger than the sum of its proper divisors (19034228).

21644872 is a wasteful number, since it uses less digits than its factorization.

21644872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6336 (or 6332 counting only the distinct ones).

The product of its digits is 21504, while the sum is 34.

The square root of 21644872 is about 4652.4049694755. The cubic root of 21644872 is about 278.6880460489.

The spelling of 21644872 in words is "twenty-one million, six hundred forty-four thousand, eight hundred seventy-two".