6640402721 has 16 divisors (see below), whose sum is σ = 6818010048. Its totient is φ = 6465355200.

The previous prime is 6640402711. The next prime is 6640402757. The reversal of 6640402721 is 1272040466.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6640402721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6640402711) 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 15 ways as a sum of consecutive naturals, for example, 2753006 + ... + 2755416.

It is an arithmetic number, because the mean of its divisors is an integer number (426125628).

Almost surely, 2^6640402721 is an apocalyptic number.

6640402721 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

6640402721 is a deficient number, since it is larger than the sum of its proper divisors (177607327).

6640402721 is a wasteful number, since it uses less digits than its factorization.

6640402721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2912.

The product of its (nonzero) digits is 16128, while the sum is 32.

The square root of 6640402721 is about 81488.6662119340. Note that the first 3 decimals coincide. The cubic root of 6640402721 is about 1879.5972731175.

The spelling of 6640402721 in words is "six billion, six hundred forty million, four hundred two thousand, seven hundred twenty-one".