21544643 has 4 divisors (see below), whose sum is σ = 21817440. Its totient is φ = 21271848.

The previous prime is 21544631. The next prime is 21544669. The reversal of 21544643 is 34644512.

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

It is a cyclic number.

It is not a de Polignac number, because 21544643 - 2¹⁰ = 21543619 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21544673) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136280 + ... + 136437.

It is an arithmetic number, because the mean of its divisors is an integer number (5454360).

Almost surely, 2^21544643 is an apocalyptic number.

21544643 is a deficient number, since it is larger than the sum of its proper divisors (272797).

21544643 is an equidigital number, since it uses as much as digits as its factorization.

21544643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 272796.

The product of its digits is 11520, while the sum is 29.

The square root of 21544643 is about 4641.6207298744. The cubic root of 21544643 is about 278.2572149730.

The spelling of 21544643 in words is "twenty-one million, five hundred forty-four thousand, six hundred forty-three".