21989779 has 12 divisors (see below), whose sum is σ = 25834224. Its totient is φ = 18661104.

The previous prime is 21989777. The next prime is 21989797. The reversal of 21989779 is 97798912.

It is not a de Polignac number, because 21989779 - 2¹ = 21989777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21989777) 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 11 ways as a sum of consecutive naturals, for example, 2869 + ... + 7225.

It is an arithmetic number, because the mean of its divisors is an integer number (2152852).

Almost surely, 2^21989779 is an apocalyptic number.

21989779 is a deficient number, since it is larger than the sum of its proper divisors (3844445).

21989779 is a wasteful number, since it uses less digits than its factorization.

21989779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4474 (or 4467 counting only the distinct ones).

The product of its digits is 571536, while the sum is 52.

The square root of 21989779 is about 4689.3260709829. The cubic root of 21989779 is about 280.1605329437.

It can be divided in two parts, 219 and 89779, that added together give a palindrome (89998).

The spelling of 21989779 in words is "twenty-one million, nine hundred eighty-nine thousand, seven hundred seventy-nine".