21664989 has 10 divisors (see below), whose sum is σ = 32363870. Its totient is φ = 14443272.

The previous prime is 21664967. The next prime is 21665009. The reversal of 21664989 is 98946612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 15539364 + 6125625 = 3942^2 + 2475^2 .

It is not a de Polignac number, because 21664989 - 2⁷ = 21664861 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 (21664789) 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 9 ways as a sum of consecutive naturals, for example, 133654 + ... + 133815.

It is an arithmetic number, because the mean of its divisors is an integer number (3236387).

Almost surely, 2^21664989 is an apocalyptic number.

It is an amenable number.

21664989 is a deficient number, since it is larger than the sum of its proper divisors (10698881).

21664989 is an equidigital number, since it uses as much as digits as its factorization.

21664989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 267481 (or 267472 counting only the distinct ones).

The product of its digits is 186624, while the sum is 45.

The square root of 21664989 is about 4654.5664674597. The cubic root of 21664989 is about 278.7743579699.

The spelling of 21664989 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred eighty-nine".