6721664 has 32 divisors (see below), whose sum is σ = 14183100. Its totient is φ = 3162112.

The previous prime is 6721661. The next prime is 6721667. The reversal of 6721664 is 4661276.

6721664 is digitally balanced in base 5, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (6721661) and next prime (6721667).

It can be written as a sum of positive squares in 2 ways, for example, as 5721664 + 1000000 = 2392^2 + 1000^2 .

It is a tau number, because it is divible by the number of its divisors (32).

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a self number, because there is not a number n which added to its sum of digits gives 6721664.

It is not an unprimeable number, because it can be changed into a prime (6721661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 632 + ... + 3720.

Almost surely, 2^6721664 is an apocalyptic number.

6721664 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6721664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (7091550).

6721664 is an abundant number, since it is smaller than the sum of its proper divisors (7461436).

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

6721664 is a wasteful number, since it uses less digits than its factorization.

6721664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3120 (or 3108 counting only the distinct ones).

The product of its digits is 12096, while the sum is 32.

The square root of 6721664 is about 2592.6172104651. The cubic root of 6721664 is about 188.7233338057.

The spelling of 6721664 in words is "six million, seven hundred twenty-one thousand, six hundred sixty-four".