20971 has 4 divisors (see below), whose sum is σ = 21352. Its totient is φ = 20592.

The previous prime is 20963. The next prime is 20981. The reversal of 20971 is 17902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 17902 = 2 ⋅8951.

It is a cyclic number.

It is not a de Polignac number, because 20971 - 2³ = 20963 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (20921) 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, 90 + ... + 223.

It is an arithmetic number, because the mean of its divisors is an integer number (5338).

2²⁰⁹⁷¹ is an apocalyptic number.

20971 is a deficient number, since it is larger than the sum of its proper divisors (381).

20971 is an equidigital number, since it uses as much as digits as its factorization.

20971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 380.

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

The square root of 20971 is about 144.8136733876. The cubic root of 20971 is about 27.5765361037.

The spelling of 20971 in words is "twenty thousand, nine hundred seventy-one".