21665271 has 4 divisors (see below), whose sum is σ = 28887032. Its totient is φ = 14443512.

The previous prime is 21665251. The next prime is 21665279. The reversal of 21665271 is 17256612.

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

It is not a de Polignac number, because 21665271 - 2⁷ = 21665143 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 (21665279) 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, 3610876 + ... + 3610881.

It is an arithmetic number, because the mean of its divisors is an integer number (7221758).

Almost surely, 2^21665271 is an apocalyptic number.

21665271 is a deficient number, since it is larger than the sum of its proper divisors (7221761).

21665271 is an equidigital number, since it uses as much as digits as its factorization.

21665271 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7221760.

The product of its digits is 5040, while the sum is 30.

The square root of 21665271 is about 4654.5967601931. The cubic root of 21665271 is about 278.7755675101.

The spelling of 21665271 in words is "twenty-one million, six hundred sixty-five thousand, two hundred seventy-one".