666666638 has 16 divisors (see below), whose sum is σ = 1138340736. Its totient is φ = 289854840.

The previous prime is 666666631. The next prime is 666666647. The reversal of 666666638 is 836666666.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 666666638.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666666631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 658256 + ... + 659267.

It is an arithmetic number, because the mean of its divisors is an integer number (71146296).

Almost surely, 2^666666638 is an apocalyptic number.

666666638 is a deficient number, since it is larger than the sum of its proper divisors (471674098).

666666638 is a wasteful number, since it uses less digits than its factorization.

666666638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1317559.

The product of its digits is 6718464, while the sum is 53.

The square root of 666666638 is about 25819.8884195885. Note that the first 3 decimals coincide. The cubic root of 666666638 is about 873.5804522150.

The spelling of 666666638 in words is "six hundred sixty-six million, six hundred sixty-six thousand, six hundred thirty-eight".