21939721 has 8 divisors (see below), whose sum is σ = 22576320. Its totient is φ = 21311472.

The previous prime is 21939713. The next prime is 21939727. The reversal of 21939721 is 12793912.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21939721 - 2³ = 21939713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21939727) 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 7 ways as a sum of consecutive naturals, for example, 3450 + ... + 7468.

It is an arithmetic number, because the mean of its divisors is an integer number (2822040).

Almost surely, 2^21939721 is an apocalyptic number.

It is an amenable number.

21939721 is a deficient number, since it is larger than the sum of its proper divisors (636599).

21939721 is a wasteful number, since it uses less digits than its factorization.

21939721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4175.

The product of its digits is 6804, while the sum is 34.

The square root of 21939721 is about 4683.9855892178. The cubic root of 21939721 is about 279.9477836303.

The spelling of 21939721 in words is "twenty-one million, nine hundred thirty-nine thousand, seven hundred twenty-one".