21664767 has 4 divisors (see below), whose sum is σ = 28886360. Its totient is φ = 14443176.

The previous prime is 21664763. The next prime is 21664771. The reversal of 21664767 is 76746612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21664763) and next prime (21664771).

It is not a de Polignac number, because 21664767 - 2² = 21664763 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664763) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3610792 + ... + 3610797.

It is an arithmetic number, because the mean of its divisors is an integer number (7221590).

Almost surely, 2^21664767 is an apocalyptic number.

21664767 is a deficient number, since it is larger than the sum of its proper divisors (7221593).

21664767 is an equidigital number, since it uses as much as digits as its factorization.

21664767 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7221592.

The product of its digits is 84672, while the sum is 39.

The square root of 21664767 is about 4654.5426198500. The cubic root of 21664767 is about 278.7734057712.

The spelling of 21664767 in words is "twenty-one million, six hundred sixty-four thousand, seven hundred sixty-seven".