20765 has 4 divisors (see below), whose sum is σ = 24924. Its totient is φ = 16608.

The previous prime is 20759. The next prime is 20771. The reversal of 20765 is 56702.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56702 = 2 ⋅28351.

It is an interprime number because it is at equal distance from previous prime (20759) and next prime (20771).

It can be written as a sum of positive squares in 2 ways, for example, as 2809 + 17956 = 53^2 + 134^2 .

It is a cyclic number.

It is not a de Polignac number, because 20765 - 2⁴ = 20749 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2072 + ... + 2081.

It is an arithmetic number, because the mean of its divisors is an integer number (6231).

2²⁰⁷⁶⁵ is an apocalyptic number.

It is an amenable number.

20765 is a deficient number, since it is larger than the sum of its proper divisors (4159).

20765 is an equidigital number, since it uses as much as digits as its factorization.

20765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4158.

The product of its (nonzero) digits is 420, while the sum is 20.

The square root of 20765 is about 144.1006592629. The cubic root of 20765 is about 27.4859432293.

Subtracting 20765 from its reverse (56702), we obtain a cube (35937 = 33³).

It can be divided in two parts, 207 and 65, that added together give a palindrome (272).

The spelling of 20765 in words is "twenty thousand, seven hundred sixty-five".