6857721 has 12 divisors (see below), whose sum is σ = 10667748. Its totient is φ = 4220064.

The previous prime is 6857713. The next prime is 6857729. The reversal of 6857721 is 1277586.

6857721 is a `hidden beast` number, since 68 + 577 + 21 = 666.

It is an interprime number because it is at equal distance from previous prime (6857713) and next prime (6857729).

It can be written as a sum of positive squares in 2 ways, for example, as 4562496 + 2295225 = 2136^2 + 1515^2 .

It is not a de Polignac number, because 6857721 - 2³ = 6857713 is a prime.

6857721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (6857729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 29190 + ... + 29423.

It is an arithmetic number, because the mean of its divisors is an integer number (888979).

Almost surely, 2^6857721 is an apocalyptic number.

It is an amenable number.

6857721 is a deficient number, since it is larger than the sum of its proper divisors (3810027).

6857721 is a wasteful number, since it uses less digits than its factorization.

6857721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58632 (or 58629 counting only the distinct ones).

The product of its digits is 23520, while the sum is 36.

The square root of 6857721 is about 2618.7250714804. The cubic root of 6857721 is about 189.9881894782.

The spelling of 6857721 in words is "six million, eight hundred fifty-seven thousand, seven hundred twenty-one".