7821 has 12 divisors (see below), whose sum is σ = 12480.
Its totient is φ = 4680.
The previous prime is 7817. The next prime is 7823. The reversal of 7821 is 1287.
It is not a de Polignac number, because 7821 - 22 = 7817 is a prime.
It is a super-2 number, since 2×78212 = 122336082, which contains 22 as substring.
It is a Curzon number.
It is a junction number, because it is equal to n+sod(n) for n = 7794 and 7803.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 7821.
It is not an unprimeable number, because it can be changed into a prime (7823) by changing a digit.
It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 60 + ... + 138.
It is an arithmetic number, because the mean of its divisors is an integer number (1040).
27821 is an apocalyptic number.
It is an amenable number.
7821 is a deficient number, since it is larger than the sum of its proper divisors (4659).
7821 is a wasteful number, since it uses less digits than its factorization.
7821 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 96 (or 93 counting only the distinct ones).
The product of its digits is 112, while the sum is 18.
The square root of 7821 is about 88.4364178379.
The cubic root of 7821 is about 19.8497067595.
It can be divided in two parts, 78 and 21, that added together give a palindrome (99).
The spelling of 7821 in words is "seven thousand, eight hundred twenty-one".