20091 has 8 divisors (see below), whose sum is σ = 27664. Its totient is φ = 12960.

The previous prime is 20089. The next prime is 20101. The reversal of 20091 is 19002.

It is a happy number.

20091 is nontrivially palindromic in base 9.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 20091 - 2¹ = 20089 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (20011) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21 + ... + 201.

It is an arithmetic number, because the mean of its divisors is an integer number (3458).

2²⁰⁰⁹¹ is an apocalyptic number.

20091 is a deficient number, since it is larger than the sum of its proper divisors (7573).

20091 is a wasteful number, since it uses less digits than its factorization.

20091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221.

The product of its (nonzero) digits is 18, while the sum is 12.

The square root of 20091 is about 141.7427246810. The cubic root of 20091 is about 27.1852825513.

Adding to 20091 its reverse (19002), we get a palindrome (39093).

Subtracting from 20091 its reverse (19002), we obtain a square (1089 = 33²).

The spelling of 20091 in words is "twenty thousand, ninety-one".