21664718 has 16 divisors (see below), whose sum is σ = 33312384. Its totient is φ = 10563960.

The previous prime is 21664717. The next prime is 21664729. The reversal of 21664718 is 81746612.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664717) 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 7 ways as a sum of consecutive naturals, for example, 13583 + ... + 15093.

It is an arithmetic number, because the mean of its divisors is an integer number (2082024).

Almost surely, 2^21664718 is an apocalyptic number.

21664718 is a deficient number, since it is larger than the sum of its proper divisors (11647666).

21664718 is a wasteful number, since it uses less digits than its factorization.

21664718 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1687.

The product of its digits is 16128, while the sum is 35.

The square root of 21664718 is about 4654.5373561719. The cubic root of 21664718 is about 278.7731956004.

The spelling of 21664718 in words is "twenty-one million, six hundred sixty-four thousand, seven hundred eighteen".