20791 has 4 divisors (see below), whose sum is σ = 22032. Its totient is φ = 19552.

The previous prime is 20789. The next prime is 20807. The reversal of 20791 is 19702.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19702 = 2 ⋅9851.

It is a cyclic number.

It is not a de Polignac number, because 20791 - 2¹ = 20789 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20731) 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, 595 + ... + 628.

It is an arithmetic number, because the mean of its divisors is an integer number (5508).

2²⁰⁷⁹¹ is an apocalyptic number.

20791 is a deficient number, since it is larger than the sum of its proper divisors (1241).

20791 is a wasteful number, since it uses less digits than its factorization.

20791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1240.

The product of its (nonzero) digits is 126, while the sum is 19.

The square root of 20791 is about 144.1908457566. The cubic root of 20791 is about 27.4974102244.

Subtracting from 20791 its reverse (19702), we obtain a square (1089 = 33²).

It can be divided in two parts, 2079 and 1, that added together give a triangular number (2080 = T₆₄).

The spelling of 20791 in words is "twenty thousand, seven hundred ninety-one".