6640921 has 12 divisors (see below), whose sum is σ = 7767732. Its totient is φ = 5660928.

The previous prime is 6640903. The next prime is 6640927. The reversal of 6640921 is 1290466.

It can be written as a sum of positive squares in 2 ways, for example, as 290521 + 6350400 = 539^2 + 2520^2 .

It is not a de Polignac number, because 6640921 - 2⁵ = 6640889 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 6640921.

It is not an unprimeable number, because it can be changed into a prime (6640927) 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 11 ways as a sum of consecutive naturals, for example, 15121 + ... + 15553.

It is an arithmetic number, because the mean of its divisors is an integer number (647311).

Almost surely, 2^6640921 is an apocalyptic number.

It is an amenable number.

6640921 is a deficient number, since it is larger than the sum of its proper divisors (1126811).

6640921 is a wasteful number, since it uses less digits than its factorization.

6640921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 760 (or 753 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 6640921 is about 2576.9984478071. The cubic root of 6640921 is about 187.9646172283.

It can be divided in two parts, 66409 and 21, that added together give a triangular number (66430 = T₃₆₄).

The spelling of 6640921 in words is "six million, six hundred forty thousand, nine hundred twenty-one".