78686777209 has 4 divisors (see below), whose sum is σ = 78687432180. Its totient is φ = 78686122240.

The previous prime is 78686777173. The next prime is 78686777219. The reversal of 78686777209 is 90277768687.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 90277768687 = 86993 ⋅1037759.

It can be written as a sum of positive squares in 2 ways, for example, as 26963282025 + 51723495184 = 164205^2 + 227428^2 .

It is a cyclic number.

It is not a de Polignac number, because 78686777209 - 2²¹ = 78684680057 is a prime.

It is a Smith number, since the sum of its digits (67) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78686777219) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 89752 + ... + 406729.

It is an arithmetic number, because the mean of its divisors is an integer number (19671858045).

Almost surely, 2^78686777209 is an apocalyptic number.

It is an amenable number.

78686777209 is a deficient number, since it is larger than the sum of its proper divisors (654971).

78686777209 is a wasteful number, since it uses less digits than its factorization.

78686777209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 654970.

The product of its (nonzero) digits is 99574272, while the sum is 67.

The spelling of 78686777209 in words is "seventy-eight billion, six hundred eighty-six million, seven hundred seventy-seven thousand, two hundred nine".