21297665 has 4 divisors (see below), whose sum is σ = 25557204. Its totient is φ = 17038128.

The previous prime is 21297659. The next prime is 21297667. The reversal of 21297665 is 56679212.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 11669056 + 9628609 = 3416^2 + 3103^2 .

It is a cyclic number.

It is not a de Polignac number, because 21297665 - 2²⁴ = 4520449 is a prime.

It is a super-3 number, since 3×21297665³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21297667) 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, 2129762 + ... + 2129771.

It is an arithmetic number, because the mean of its divisors is an integer number (6389301).

Almost surely, 2^21297665 is an apocalyptic number.

It is an amenable number.

21297665 is a deficient number, since it is larger than the sum of its proper divisors (4259539).

21297665 is an equidigital number, since it uses as much as digits as its factorization.

21297665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4259538.

The product of its digits is 45360, while the sum is 38.

The square root of 21297665 is about 4614.9393278785. The cubic root of 21297665 is about 277.1898545095.

The spelling of 21297665 in words is "twenty-one million, two hundred ninety-seven thousand, six hundred sixty-five".