666438661 has 24 divisors (see below), whose sum is σ = 819012480. Its totient is φ = 539203392.

The previous prime is 666438649. The next prime is 666438671. The reversal of 666438661 is 166834666.

It is not a de Polignac number, because 666438661 - 2⁵ = 666438629 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666438611) 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 23 ways as a sum of consecutive naturals, for example, 290260 + ... + 292546.

It is an arithmetic number, because the mean of its divisors is an integer number (34125520).

Almost surely, 2^666438661 is an apocalyptic number.

It is an amenable number.

666438661 is a deficient number, since it is larger than the sum of its proper divisors (152573819).

666438661 is a wasteful number, since it uses less digits than its factorization.

666438661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2633 (or 2626 counting only the distinct ones).

The product of its digits is 746496, while the sum is 46.

The square root of 666438661 is about 25815.4732863839. The cubic root of 666438661 is about 873.4808627324.

The spelling of 666438661 in words is "six hundred sixty-six million, four hundred thirty-eight thousand, six hundred sixty-one".