6656721 has 4 divisors (see below), whose sum is σ = 8875632. Its totient is φ = 4437812.

The previous prime is 6656711. The next prime is 6656737. The reversal of 6656721 is 1276566.

6656721 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6656721 is a prime.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (6656711) 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 3 ways as a sum of consecutive naturals, for example, 1109451 + ... + 1109456.

It is an arithmetic number, because the mean of its divisors is an integer number (2218908).

Almost surely, 2^6656721 is an apocalyptic number.

It is an amenable number.

6656721 is a deficient number, since it is larger than the sum of its proper divisors (2218911).

6656721 is a wasteful number, since it uses less digits than its factorization.

6656721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2218910.

The product of its digits is 15120, while the sum is 33.

The square root of 6656721 is about 2580.0622085523. The cubic root of 6656721 is about 188.1135668891.

The spelling of 6656721 in words is "six million, six hundred fifty-six thousand, seven hundred twenty-one".