21664039 has 4 divisors (see below), whose sum is σ = 22125024. Its totient is φ = 21203056.

The previous prime is 21664037. The next prime is 21664051. The reversal of 21664039 is 93046612.

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 21664039 - 2¹ = 21664037 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21664039.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664037) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 230422 + ... + 230515.

It is an arithmetic number, because the mean of its divisors is an integer number (5531256).

Almost surely, 2^21664039 is an apocalyptic number.

21664039 is a deficient number, since it is larger than the sum of its proper divisors (460985).

21664039 is an equidigital number, since it uses as much as digits as its factorization.

21664039 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 460984.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 21664039 is about 4654.4644160204. The cubic root of 21664039 is about 278.7702832003.

The spelling of 21664039 in words is "twenty-one million, six hundred sixty-four thousand, thirty-nine".