21820989 has 4 divisors (see below), whose sum is σ = 29094656. Its totient is φ = 14547324.

The previous prime is 21820957. The next prime is 21820991. The reversal of 21820989 is 98902812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21820989 - 2⁵ = 21820957 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 (21820999) 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, 3636829 + ... + 3636834.

It is an arithmetic number, because the mean of its divisors is an integer number (7273664).

Almost surely, 2^21820989 is an apocalyptic number.

It is an amenable number.

21820989 is a deficient number, since it is larger than the sum of its proper divisors (7273667).

21820989 is an equidigital number, since it uses as much as digits as its factorization.

21820989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7273666.

The product of its (nonzero) digits is 20736, while the sum is 39.

The square root of 21820989 is about 4671.2941461655. The cubic root of 21820989 is about 279.4418686435.

The spelling of 21820989 in words is "twenty-one million, eight hundred twenty thousand, nine hundred eighty-nine".