20861 has 4 divisors (see below), whose sum is σ = 21792. Its totient is φ = 19932.

The previous prime is 20857. The next prime is 20873. The reversal of 20861 is 16802.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20861 - 2² = 20857 is a prime.

It is a magnanimous number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20161) 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, 431 + ... + 476.

It is an arithmetic number, because the mean of its divisors is an integer number (5448).

2²⁰⁸⁶¹ is an apocalyptic number.

It is an amenable number.

20861 is a deficient number, since it is larger than the sum of its proper divisors (931).

20861 is an equidigital number, since it uses as much as digits as its factorization.

20861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 930.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 20861 is about 144.4333756443. The cubic root of 20861 is about 27.5282354623.

The spelling of 20861 in words is "twenty thousand, eight hundred sixty-one".