21665297 has 4 divisors (see below), whose sum is σ = 21736176. Its totient is φ = 21594420.

The previous prime is 21665279. The next prime is 21665341. The reversal of 21665297 is 79256612.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 21665297 - 2⁸ = 21665041 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 21665297.

It is not an unprimeable number, because it can be changed into a prime (21665227) 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, 34979 + ... + 35592.

It is an arithmetic number, because the mean of its divisors is an integer number (5434044).

Almost surely, 2^21665297 is an apocalyptic number.

It is an amenable number.

21665297 is a deficient number, since it is larger than the sum of its proper divisors (70879).

21665297 is an equidigital number, since it uses as much as digits as its factorization.

21665297 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70878.

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

The square root of 21665297 is about 4654.5995531302. The cubic root of 21665297 is about 278.7756790275.

The spelling of 21665297 in words is "twenty-one million, six hundred sixty-five thousand, two hundred ninety-seven".