20565 has 12 divisors (see below), whose sum is σ = 35724. Its totient is φ = 10944.

The previous prime is 20563. The next prime is 20593. The reversal of 20565 is 56502.

It can be written as a sum of positive squares in 2 ways, for example, as 12996 + 7569 = 114^2 + 87^2 .

It is not a de Polignac number, because 20565 - 2¹ = 20563 is a prime.

20565 is a Rhonda number in base 14.

It is a Curzon number.

It is a nialpdrome in base 12.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20563) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 184 + ... + 273.

It is an arithmetic number, because the mean of its divisors is an integer number (2977).

2²⁰⁵⁶⁵ is an apocalyptic number.

It is an amenable number.

20565 is a deficient number, since it is larger than the sum of its proper divisors (15159).

20565 is a wasteful number, since it uses less digits than its factorization.

20565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 468 (or 465 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 20565 is about 143.4050208326. The cubic root of 20565 is about 27.3974139318.

Subtracting 20565 from its reverse (56502), we obtain a cube (35937 = 33³).

It can be divided in two parts, 20 and 565, that added together give a palindrome (585).

The spelling of 20565 in words is "twenty thousand, five hundred sixty-five".