21660165 has 24 divisors (see below), whose sum is σ = 38757888. Its totient is φ = 11178720.

The previous prime is 21660161. The next prime is 21660167. The reversal of 21660165 is 56106612.

It is a happy number.

It is not a de Polignac number, because 21660165 - 2² = 21660161 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660161) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6369 + ... + 9158.

It is an arithmetic number, because the mean of its divisors is an integer number (1614912).

Almost surely, 2^21660165 is an apocalyptic number.

It is an amenable number.

21660165 is a deficient number, since it is larger than the sum of its proper divisors (17097723).

21660165 is a wasteful number, since it uses less digits than its factorization.

21660165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15569 (or 15566 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21660165 is about 4654.0482378248. The cubic root of 21660165 is about 278.7536654857.

Adding to 21660165 its reverse (56106612), we get a palindrome (77766777).

The spelling of 21660165 in words is "twenty-one million, six hundred sixty thousand, one hundred sixty-five".