6921 has 6 divisors (see below), whose sum is σ = 10010.
Its totient is φ = 4608.
The previous prime is 6917. The next prime is 6947. The reversal of 6921 is 1296.
Subtracting from 6921 its sum of digits (18), we obtain a triangular number (6903 = T117).
Subtracting from 6921 its reverse (1296), we obtain a square (5625 = 752).
It can be written as a sum of positive squares in only one way, i.e., 5625 + 1296 = 75^2 + 36^2
It is not a de Polignac number, because 6921 - 22 = 6917 is a prime.
It is an alternating number because its digits alternate between even and odd.
It is a Duffinian number.
6921 is a lucky number.
It is a nialpdrome in base 11.
It is a junction number, because it is equal to n+sod(n) for n = 6894 and 6903.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 6921.
It is not an unprimeable number, because it can be changed into a prime (6911) by changing a digit.
It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 376 + ... + 393.
It is an amenable number.
6921 is a deficient number, since it is larger than the sum of its proper divisors (3089).
6921 is a wasteful number, since it uses less digits than its factorization.
6921 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 775 (or 772 counting only the distinct ones).
The product of its digits is 108, while the sum is 18.
The square root of 6921 is about 83.1925477432.
The cubic root of 6921 is about 19.0570767516.
The spelling of 6921 in words is "six thousand, nine hundred twenty-one".