777991 has 4 divisors (see below), whose sum is σ = 794592. Its totient is φ = 761392.

The previous prime is 777989. The next prime is 778013. The reversal of 777991 is 199777.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 777991 - 2¹ = 777989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (777901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8230 + ... + 8323.

It is an arithmetic number, because the mean of its divisors is an integer number (198648).

2⁷⁷⁷⁹⁹¹ is an apocalyptic number.

777991 is a deficient number, since it is larger than the sum of its proper divisors (16601).

777991 is a wasteful number, since it uses less digits than its factorization.

777991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16600.

The product of its digits is 27783, while the sum is 40.

The square root of 777991 is about 882.0379810416. The cubic root of 777991 is about 91.9725422155.

The spelling of 777991 in words is "seven hundred seventy-seven thousand, nine hundred ninety-one".