21989221 has 8 divisors (see below), whose sum is σ = 22984920. Its totient is φ = 21009408.

The previous prime is 21989207. The next prime is 21989237. The reversal of 21989221 is 12298912.

It can be written as a sum of positive squares in 4 ways, for example, as 2500 + 21986721 = 50^2 + 4689^2 .

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 21989221 - 2⁹ = 21988709 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 (21989281) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1096 + ... + 6721.

It is an arithmetic number, because the mean of its divisors is an integer number (2873115).

Almost surely, 2^21989221 is an apocalyptic number.

It is an amenable number.

21989221 is a deficient number, since it is larger than the sum of its proper divisors (995699).

21989221 is an equidigital number, since it uses as much as digits as its factorization.

21989221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7943.

The product of its digits is 5184, while the sum is 34.

The square root of 21989221 is about 4689.2665737832. The cubic root of 21989221 is about 280.1581631928.

The spelling of 21989221 in words is "twenty-one million, nine hundred eighty-nine thousand, two hundred twenty-one".