666666778 has 16 divisors (see below), whose sum is σ = 1010359656. Its totient is φ = 329889280.

The previous prime is 666666773. The next prime is 666666809. The reversal of 666666778 is 877666666.

It can be written as a sum of positive squares in 4 ways, for example, as 238300969 + 428365809 = 15437^2 + 20697^2 .

It is a plaindrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (666666773) 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, 183750 + ... + 187342.

Almost surely, 2^666666778 is an apocalyptic number.

666666778 is a deficient number, since it is larger than the sum of its proper divisors (343692878).

666666778 is a wasteful number, since it uses less digits than its factorization.

666666778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4529.

The product of its digits is 18289152, while the sum is 58.

The square root of 666666778 is about 25819.8911306768. The cubic root of 666666778 is about 873.5805133656.

The spelling of 666666778 in words is "six hundred sixty-six million, six hundred sixty-six thousand, seven hundred seventy-eight".