21668518 has 8 divisors (see below), whose sum is σ = 32559912. Its totient is φ = 10815216.

The previous prime is 21668501. The next prime is 21668519. The reversal of 21668518 is 81586612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21668519) 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, 8055 + ... + 10402.

It is an arithmetic number, because the mean of its divisors is an integer number (4069989).

Almost surely, 2^21668518 is an apocalyptic number.

21668518 is a deficient number, since it is larger than the sum of its proper divisors (10891394).

21668518 is a wasteful number, since it uses less digits than its factorization.

21668518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19046.

The product of its digits is 23040, while the sum is 37.

The square root of 21668518 is about 4654.9455421090. The cubic root of 21668518 is about 278.7894936233.

The spelling of 21668518 in words is "twenty-one million, six hundred sixty-eight thousand, five hundred eighteen".