21989791 has 4 divisors (see below), whose sum is σ = 22157784. Its totient is φ = 21821800.

The previous prime is 21989777. The next prime is 21989797. The reversal of 21989791 is 19798912.

It is a happy number.

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 21989791 - 2¹⁹ = 21465503 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 (21989797) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 83800 + ... + 84061.

It is an arithmetic number, because the mean of its divisors is an integer number (5539446).

Almost surely, 2^21989791 is an apocalyptic number.

21989791 is a deficient number, since it is larger than the sum of its proper divisors (167993).

21989791 is a wasteful number, since it uses less digits than its factorization.

21989791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 167992.

The product of its digits is 81648, while the sum is 46.

The square root of 21989791 is about 4689.3273504843. The cubic root of 21989791 is about 280.1605839057.

The spelling of 21989791 in words is "twenty-one million, nine hundred eighty-nine thousand, seven hundred ninety-one".