79921 has 4 divisors (see below), whose sum is σ = 80500. Its totient is φ = 79344.

The previous prime is 79907. The next prime is 79939. The reversal of 79921 is 12997.

79921 is nontrivially palindromic in base 16.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12997 = 41 ⋅317.

It can be written as a sum of positive squares in 2 ways, for example, as 67600 + 12321 = 260^2 + 111^2 .

It is a cyclic number.

It is not a de Polignac number, because 79921 - 2⁵ = 79889 is a prime.

It is a Duffinian number.

79921 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 79921.

It is not an unprimeable number, because it can be changed into a prime (79901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55 + ... + 403.

It is an arithmetic number, because the mean of its divisors is an integer number (20125).

2⁷⁹⁹²¹ is an apocalyptic number.

It is an amenable number.

79921 is a deficient number, since it is larger than the sum of its proper divisors (579).

79921 is a wasteful number, since it uses less digits than its factorization.

79921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 578.

The product of its digits is 1134, while the sum is 28.

The square root of 79921 is about 282.7030243913. The cubic root of 79921 is about 43.0745057677.

Subtracting from 79921 its product of digits (1134), we obtain a palindrome (78787).

It can be divided in two parts, 799 and 21, that added together give a triangular number (820 = T₄₀).

The spelling of 79921 in words is "seventy-nine thousand, nine hundred twenty-one".