21664259 has 4 divisors (see below), whose sum is σ = 21673680. Its totient is φ = 21654840.

The previous prime is 21664207. The next prime is 21664267. The reversal of 21664259 is 95246612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21664259 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664759) 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, 1274 + ... + 6704.

It is an arithmetic number, because the mean of its divisors is an integer number (5418420).

Almost surely, 2^21664259 is an apocalyptic number.

21664259 is a deficient number, since it is larger than the sum of its proper divisors (9421).

21664259 is an equidigital number, since it uses as much as digits as its factorization.

21664259 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9420.

The product of its digits is 25920, while the sum is 35.

The square root of 21664259 is about 4654.4880491844. The cubic root of 21664259 is about 278.7712268418.

The spelling of 21664259 in words is "twenty-one million, six hundred sixty-four thousand, two hundred fifty-nine".