20665565 has 4 divisors (see below), whose sum is σ = 24798684. Its totient is φ = 16532448.

The previous prime is 20665549. The next prime is 20665577. The reversal of 20665565 is 56556602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56556602 = 2 ⋅28278301.

It can be written as a sum of positive squares in 2 ways, for example, as 13380964 + 7284601 = 3658^2 + 2699^2 .

It is a cyclic number.

It is not a de Polignac number, because 20665565 - 2⁴ = 20665549 is a prime.

It is a Duffinian number.

It is a congruent 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, 2066552 + ... + 2066561.

It is an arithmetic number, because the mean of its divisors is an integer number (6199671).

Almost surely, 2^20665565 is an apocalyptic number.

It is an amenable number.

20665565 is a deficient number, since it is larger than the sum of its proper divisors (4133119).

20665565 is an equidigital number, since it uses as much as digits as its factorization.

20665565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4133118.

The product of its (nonzero) digits is 54000, while the sum is 35.

The square root of 20665565 is about 4545.9393968684. The cubic root of 20665565 is about 274.4200007308.

The spelling of 20665565 in words is "twenty million, six hundred sixty-five thousand, five hundred sixty-five".