20591 has 4 divisors (see below), whose sum is σ = 21000. Its totient is φ = 20184.

The previous prime is 20563. The next prime is 20593. The reversal of 20591 is 19502.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20591 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20591.

It is not an unprimeable number, because it can be changed into a prime (20593) 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, 116 + ... + 233.

It is an arithmetic number, because the mean of its divisors is an integer number (5250).

2²⁰⁵⁹¹ is an apocalyptic number.

20591 is a deficient number, since it is larger than the sum of its proper divisors (409).

20591 is an equidigital number, since it uses as much as digits as its factorization.

20591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408.

The product of its (nonzero) digits is 90, while the sum is 17.

The square root of 20591 is about 143.4956445332. The cubic root of 20591 is about 27.4089551065.

Subtracting from 20591 its reverse (19502), we obtain a square (1089 = 33²).

The spelling of 20591 in words is "twenty thousand, five hundred ninety-one".