21731665 has 16 divisors (see below), whose sum is σ = 27495936. Its totient is φ = 16456000.

The previous prime is 21731653. The next prime is 21731669. The reversal of 21731665 is 56613712.

It is not a de Polignac number, because 21731665 - 2¹⁹ = 21207377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21731669) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10680 + ... + 12550.

It is an arithmetic number, because the mean of its divisors is an integer number (1718496).

Almost surely, 2^21731665 is an apocalyptic number.

It is an amenable number.

21731665 is a deficient number, since it is larger than the sum of its proper divisors (5764271).

21731665 is a wasteful number, since it uses less digits than its factorization.

21731665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2000.

The product of its digits is 7560, while the sum is 31.

The square root of 21731665 is about 4661.7233937676. The cubic root of 21731665 is about 279.0600496807.

The spelling of 21731665 in words is "twenty-one million, seven hundred thirty-one thousand, six hundred sixty-five".