21664691 has 8 divisors (see below), whose sum is σ = 22425600. Its totient is φ = 20907720.

The previous prime is 21664667. The next prime is 21664703. The reversal of 21664691 is 19646612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21664691 is a prime.

It is a super-2 number, since 2×21664691² = 938717672250962, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664661) 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, 14120 + ... + 15578.

It is an arithmetic number, because the mean of its divisors is an integer number (2803200).

Almost surely, 2^21664691 is an apocalyptic number.

21664691 is a deficient number, since it is larger than the sum of its proper divisors (760909).

21664691 is a wasteful number, since it uses less digits than its factorization.

21664691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1969.

The product of its digits is 15552, while the sum is 35.

The square root of 21664691 is about 4654.5344557754. The cubic root of 21664691 is about 278.7730797918.

The spelling of 21664691 in words is "twenty-one million, six hundred sixty-four thousand, six hundred ninety-one".