21491668 has 24 divisors (see below), whose sum is σ = 42446880. Its totient is φ = 9431520.

The previous prime is 21491663. The next prime is 21491669. The reversal of 21491668 is 86619412.

It is a happy number.

It is a hoax number, since the sum of its digits (37) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21491663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7146 + ... + 9697.

It is an arithmetic number, because the mean of its divisors is an integer number (1768620).

Almost surely, 2^21491668 is an apocalyptic number.

It is an amenable number.

21491668 is a deficient number, since it is larger than the sum of its proper divisors (20955212).

21491668 is a wasteful number, since it uses less digits than its factorization.

21491668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16887 (or 16885 counting only the distinct ones).

The product of its digits is 20736, while the sum is 37.

The square root of 21491668 is about 4635.9106980182. The cubic root of 21491668 is about 278.0289637369.

The spelling of 21491668 in words is "twenty-one million, four hundred ninety-one thousand, six hundred sixty-eight".