21664978 has 8 divisors (see below), whose sum is σ = 34207920. Its totient is φ = 10262340.

The previous prime is 21664967. The next prime is 21665009. The reversal of 21664978 is 87946612.

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

It is an unprimeable number.

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, 285028 + ... + 285103.

It is an arithmetic number, because the mean of its divisors is an integer number (4275990).

Almost surely, 2^21664978 is an apocalyptic number.

21664978 is a deficient number, since it is larger than the sum of its proper divisors (12542942).

21664978 is a wasteful number, since it uses less digits than its factorization.

21664978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570152.

The product of its digits is 145152, while the sum is 43.

The square root of 21664978 is about 4654.5652858242. The cubic root of 21664978 is about 278.7743107890.

The spelling of 21664978 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred seventy-eight".