6639864 has 64 divisors (see below), whose sum is σ = 20701440. Its totient is φ = 1724160.

The previous prime is 6639863. The next prime is 6639881. The reversal of 6639864 is 4689366.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6639863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 52 + ... + 3644.

It is an arithmetic number, because the mean of its divisors is an integer number (323460).

Almost surely, 2^6639864 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6639864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (10350720).

6639864 is an abundant number, since it is smaller than the sum of its proper divisors (14061576).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

6639864 is a wasteful number, since it uses less digits than its factorization.

6639864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3620 (or 3616 counting only the distinct ones).

The product of its digits is 186624, while the sum is 42.

The square root of 6639864 is about 2576.7933560920. The cubic root of 6639864 is about 187.9546442571.

It can be divided in two parts, 6639 and 864, that added together give a triangular number (7503 = T₁₂₂).

The spelling of 6639864 in words is "six million, six hundred thirty-nine thousand, eight hundred sixty-four".