6639813 has 10 divisors (see below), whose sum is σ = 9918854. Its totient is φ = 4426488.

The previous prime is 6639803. The next prime is 6639817. The reversal of 6639813 is 3189366.

It is a happy number.

6639813 is a `hidden beast` number, since 6 + 639 + 8 + 13 = 666.

It can be written as a sum of positive squares in only one way, i.e., 4743684 + 1896129 = 2178^2 + 1377^2 .

It is not a de Polignac number, because 6639813 - 2¹⁷ = 6508741 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6639817) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 40906 + ... + 41067.

Almost surely, 2^6639813 is an apocalyptic number.

It is an amenable number.

6639813 is a deficient number, since it is larger than the sum of its proper divisors (3279041).

6639813 is an equidigital number, since it uses as much as digits as its factorization.

6639813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81985 (or 81976 counting only the distinct ones).

The product of its digits is 23328, while the sum is 36.

The square root of 6639813 is about 2576.7834600525. The cubic root of 6639813 is about 187.9541630368.

The spelling of 6639813 in words is "six million, six hundred thirty-nine thousand, eight hundred thirteen".