21258665 has 4 divisors (see below), whose sum is σ = 25510404. Its totient is φ = 17006928.

The previous prime is 21258661. The next prime is 21258667. The reversal of 21258665 is 56685212.

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 2483776 + 18774889 = 1576^2 + 4333^2 .

It is a cyclic number.

It is not a de Polignac number, because 21258665 - 2² = 21258661 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21258661) 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, 2125862 + ... + 2125871.

It is an arithmetic number, because the mean of its divisors is an integer number (6377601).

Almost surely, 2^21258665 is an apocalyptic number.

It is an amenable number.

21258665 is a deficient number, since it is larger than the sum of its proper divisors (4251739).

21258665 is an equidigital number, since it uses as much as digits as its factorization.

21258665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4251738.

The product of its digits is 28800, while the sum is 35.

The square root of 21258665 is about 4610.7119840649. The cubic root of 21258665 is about 277.0205556737.

The spelling of 21258665 in words is "twenty-one million, two hundred fifty-eight thousand, six hundred sixty-five".