21664173 has 4 divisors (see below), whose sum is σ = 28885568. Its totient is φ = 14442780.

The previous prime is 21664169. The next prime is 21664177. The reversal of 21664173 is 37146612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21664169) and next prime (21664177).

It is not a de Polignac number, because 21664173 - 2² = 21664169 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21664173.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664177) 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, 3610693 + ... + 3610698.

It is an arithmetic number, because the mean of its divisors is an integer number (7221392).

Almost surely, 2^21664173 is an apocalyptic number.

It is an amenable number.

21664173 is a deficient number, since it is larger than the sum of its proper divisors (7221395).

21664173 is an equidigital number, since it uses as much as digits as its factorization.

21664173 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7221394.

The product of its digits is 6048, while the sum is 30.

The square root of 21664173 is about 4654.4788107800. The cubic root of 21664173 is about 278.7708579645.

The spelling of 21664173 in words is "twenty-one million, six hundred sixty-four thousand, one hundred seventy-three".