6721 has 8 divisors (see below), whose sum is σ = 8064. Its totient is φ = 5520.

The previous prime is 6719. The next prime is 6733. The reversal of 6721 is 1276.

6721 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 6721 - 2¹ = 6719 is a prime.

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 6695 and 6704.

It is not an unprimeable number, because it can be changed into a prime (6701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 120 + ... + 166.

It is an arithmetic number, because the mean of its divisors is an integer number (1008).

2⁶⁷²¹ is an apocalyptic number.

It is an amenable number.

6721 is a deficient number, since it is larger than the sum of its proper divisors (1343).

6721 is a wasteful number, since it uses less digits than its factorization.

6721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71.

The product of its digits is 84, while the sum is 16.

The square root of 6721 is about 81.9817052762. The cubic root of 6721 is about 18.8717119252.

Adding to 6721 its reverse (1276), we get a palindrome (7997).

Subtracting from 6721 its reverse (1276), we obtain a palindrome (5445).

It can be divided in two parts, 67 and 21, that added together give a palindrome (88).

The spelling of 6721 in words is "six thousand, seven hundred twenty-one".