78728642665 has 4 divisors (see below), whose sum is σ = 94474371204. Its totient is φ = 62982914128.

The previous prime is 78728642653. The next prime is 78728642689. The reversal of 78728642665 is 56624682787.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56624682787 = 2909 ⋅19465343.

It can be written as a sum of positive squares in 2 ways, for example, as 51005060649 + 27723582016 = 225843^2 + 166504^2 .

It is a cyclic number.

It is not a de Polignac number, because 78728642665 - 2¹³ = 78728634473 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7872864262 + ... + 7872864271.

It is an arithmetic number, because the mean of its divisors is an integer number (23618592801).

Almost surely, 2^78728642665 is an apocalyptic number.

It is an amenable number.

78728642665 is a deficient number, since it is larger than the sum of its proper divisors (15745728539).

78728642665 is a wasteful number, since it uses less digits than its factorization.

78728642665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15745728538.

The product of its digits is 54190080, while the sum is 61.

The spelling of 78728642665 in words is "seventy-eight billion, seven hundred twenty-eight million, six hundred forty-two thousand, six hundred sixty-five".