21065665 has 4 divisors (see below), whose sum is σ = 25278804. Its totient is φ = 16852528.

The previous prime is 21065641. The next prime is 21065701. The reversal of 21065665 is 56656012.

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 3701776 + 17363889 = 1924^2 + 4167^2 .

It is a cyclic number.

It is not a de Polignac number, because 21065665 - 2⁹ = 21065153 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2106562 + ... + 2106571.

It is an arithmetic number, because the mean of its divisors is an integer number (6319701).

Almost surely, 2^21065665 is an apocalyptic number.

It is an amenable number.

21065665 is a deficient number, since it is larger than the sum of its proper divisors (4213139).

21065665 is an equidigital number, since it uses as much as digits as its factorization.

21065665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4213138.

The product of its (nonzero) digits is 10800, while the sum is 31.

The square root of 21065665 is about 4589.7347417906. The cubic root of 21065665 is about 276.1796815351.

The spelling of 21065665 in words is "twenty-one million, sixty-five thousand, six hundred sixty-five".