21644143 has 4 divisors (see below), whose sum is σ = 21765240. Its totient is φ = 21523048.

The previous prime is 21644113. The next prime is 21644153. The reversal of 21644143 is 34144612.

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-21644143 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644113) 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, 60280 + ... + 60637.

It is an arithmetic number, because the mean of its divisors is an integer number (5441310).

Almost surely, 2^21644143 is an apocalyptic number.

21644143 is a deficient number, since it is larger than the sum of its proper divisors (121097).

21644143 is a wasteful number, since it uses less digits than its factorization.

21644143 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 121096.

The product of its digits is 2304, while the sum is 25.

The square root of 21644143 is about 4652.3266222397. The cubic root of 21644143 is about 278.6849172729.

Adding to 21644143 its reverse (34144612), we get a palindrome (55788755).

The spelling of 21644143 in words is "twenty-one million, six hundred forty-four thousand, one hundred forty-three".