7921 has 3 divisors (see below), whose sum is σ = 8011.
Its totient is φ = 7832.
The previous prime is 7919. The next prime is 7927. The reversal of 7921 is 1297.
It can be divided in two parts, 79 and 21, that added together give a square (100 = 102).
7921 = T88 + T89.
The square root of 7921 is 89.
It is a perfect power (a square), and thus also a powerful number.
7921 is nontrivially palindromic in base 3.
7921 is an esthetic number in base 3, because in such base its adjacent digits differ by 1.
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.
It can be written as a sum of positive squares in only one way, i.e., 1521 + 6400 = 39^2 + 80^2
It is not a de Polignac number, because 7921 - 21 = 7919 is a prime.
It is a Duffinian number.
7921 is a lucky number.
It is not an unprimeable number, because it can be changed into a prime (7927) by changing a digit.
It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 45 + ... + 133.
27921 is an apocalyptic number.
7921 is the 89-th square number.
7921 is the 45-th centered octagonal number.
It is an amenable number.
7921 is a deficient number, since it is larger than the sum of its proper divisors (90).
7921 is an frugal number, since it uses more digits than its factorization.
7921 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 178 (or 89 counting only the distinct ones).
The product of its digits is 126, while the sum is 19.
The cubic root of 7921 is about 19.9339487685.
The spelling of 7921 in words is "seven thousand, nine hundred twenty-one".