21644443 has 4 divisors (see below), whose sum is σ = 21713040. Its totient is φ = 21575848.

The previous prime is 21644429. The next prime is 21644459. The reversal of 21644443 is 34444612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21644443 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21644423) 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 3 ways as a sum of consecutive naturals, for example, 33823 + ... + 34456.

It is an arithmetic number, because the mean of its divisors is an integer number (5428260).

Almost surely, 2^21644443 is an apocalyptic number.

21644443 is a deficient number, since it is larger than the sum of its proper divisors (68597).

21644443 is an equidigital number, since it uses as much as digits as its factorization.

21644443 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68596.

The product of its digits is 9216, while the sum is 28.

The square root of 21644443 is about 4652.3588640603. The cubic root of 21644443 is about 278.6862048436.

The spelling of 21644443 in words is "twenty-one million, six hundred forty-four thousand, four hundred forty-three".