6639021 has 12 divisors (see below), whose sum is σ = 9849372. Its totient is φ = 4306176.

The previous prime is 6639013. The next prime is 6639041. The reversal of 6639021 is 1209366.

It is a happy number.

6639021 is a `hidden beast` number, since 6 + 639 + 0 + 21 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 3663396 + 2975625 = 1914^2 + 1725^2 .

It is not a de Polignac number, because 6639021 - 2³ = 6639013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6639001) 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, 9636 + ... + 10301.

It is an arithmetic number, because the mean of its divisors is an integer number (820781).

Almost surely, 2^6639021 is an apocalyptic number.

It is an amenable number.

6639021 is a deficient number, since it is larger than the sum of its proper divisors (3210351).

6639021 is a wasteful number, since it uses less digits than its factorization.

6639021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19980 (or 19977 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 27.

The square root of 6639021 is about 2576.6297755013. The cubic root of 6639021 is about 187.9466896528.

The spelling of 6639021 in words is "six million, six hundred thirty-nine thousand, twenty-one".