6659721 has 6 divisors (see below), whose sum is σ = 9619610. Its totient is φ = 4439808.

The previous prime is 6659713. The next prime is 6659749. The reversal of 6659721 is 1279566.

6659721 is a `hidden beast` number, since 66 + 597 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 5588496 + 1071225 = 2364^2 + 1035^2 .

It is not a de Polignac number, because 6659721 - 2³ = 6659713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6659021) 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, 369976 + ... + 369993.

Almost surely, 2^6659721 is an apocalyptic number.

It is an amenable number.

6659721 is a deficient number, since it is larger than the sum of its proper divisors (2959889).

6659721 is a wasteful number, since it uses less digits than its factorization.

6659721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 739975 (or 739972 counting only the distinct ones).

The product of its digits is 22680, while the sum is 36.

The square root of 6659721 is about 2580.6435243946. The cubic root of 6659721 is about 188.1418218384.

The spelling of 6659721 in words is "six million, six hundred fifty-nine thousand, seven hundred twenty-one".