665307778 has 4 divisors (see below), whose sum is σ = 997961670. Its totient is φ = 332653888.

The previous prime is 665307761. The next prime is 665307787. The reversal of 665307778 is 877703566.

665307778 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 349428249 + 315879529 = 18693^2 + 17773^2 .

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 166326943 + ... + 166326946.

Almost surely, 2^665307778 is an apocalyptic number.

665307778 is a deficient number, since it is larger than the sum of its proper divisors (332653892).

665307778 is a wasteful number, since it uses less digits than its factorization.

665307778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332653891.

The product of its (nonzero) digits is 1481760, while the sum is 49.

The square root of 665307778 is about 25793.5607855914. The cubic root of 665307778 is about 872.9865116988.

The spelling of 665307778 in words is "six hundred sixty-five million, three hundred seven thousand, seven hundred seventy-eight".