21668990 has 64 divisors (see below), whose sum is σ = 47748096. Its totient is φ = 6918912.

The previous prime is 21668963. The next prime is 21669007. The reversal of 21668990 is 9986612.

It is a congruent number.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 69074 + ... + 69386.

It is an arithmetic number, because the mean of its divisors is an integer number (746064).

Almost surely, 2^21668990 is an apocalyptic number.

21668990 is an abundant number, since it is smaller than the sum of its proper divisors (26079106).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21668990 is a wasteful number, since it uses less digits than its factorization.

21668990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 393.

The product of its (nonzero) digits is 46656, while the sum is 41.

The square root of 21668990 is about 4654.9962406000. The cubic root of 21668990 is about 278.7915178763.

The spelling of 21668990 in words is "twenty-one million, six hundred sixty-eight thousand, nine hundred ninety".