21729943 has 4 divisors (see below), whose sum is σ = 21752248. Its totient is φ = 21707640.

The previous prime is 21729941. The next prime is 21729971. The reversal of 21729943 is 34992712.

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 21729943 - 2¹ = 21729941 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 (21729941) 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, 9621 + ... + 11662.

It is an arithmetic number, because the mean of its divisors is an integer number (5438062).

Almost surely, 2^21729943 is an apocalyptic number.

21729943 is a deficient number, since it is larger than the sum of its proper divisors (22305).

21729943 is a wasteful number, since it uses less digits than its factorization.

21729943 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22304.

The product of its digits is 27216, while the sum is 37.

The square root of 21729943 is about 4661.5386944656. The cubic root of 21729943 is about 279.0526786533.

The spelling of 21729943 in words is "twenty-one million, seven hundred twenty-nine thousand, nine hundred forty-three".