21644491 has 16 divisors (see below), whose sum is σ = 24208128. Its totient is φ = 19188000.

The previous prime is 21644489. The next prime is 21644507. The reversal of 21644491 is 19444612.

It is a cyclic number.

It is not a de Polignac number, because 21644491 - 2¹ = 21644489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21644461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 137785 + ... + 137941.

It is an arithmetic number, because the mean of its divisors is an integer number (1513008).

Almost surely, 2^21644491 is an apocalyptic number.

21644491 is a deficient number, since it is larger than the sum of its proper divisors (2563637).

21644491 is a wasteful number, since it uses less digits than its factorization.

21644491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 402.

The product of its digits is 6912, while the sum is 31.

The square root of 21644491 is about 4652.3640227308. The cubic root of 21644491 is about 278.6864108538.

The spelling of 21644491 in words is "twenty-one million, six hundred forty-four thousand, four hundred ninety-one".