77809991 has 6 divisors (see below), whose sum is σ = 90513720. Its totient is φ = 66694236.

The previous prime is 77809973. The next prime is 77809993. The reversal of 77809991 is 19990877.

It is not a de Polignac number, because 77809991 - 2¹⁰ = 77808967 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 (77809993) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 793931 + ... + 794028.

It is an arithmetic number, because the mean of its divisors is an integer number (15085620).

Almost surely, 2^77809991 is an apocalyptic number.

77809991 is a deficient number, since it is larger than the sum of its proper divisors (12703729).

77809991 is a wasteful number, since it uses less digits than its factorization.

77809991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1587973 (or 1587966 counting only the distinct ones).

The product of its (nonzero) digits is 285768, while the sum is 50.

The square root of 77809991 is about 8820.9971658538. The cubic root of 77809991 is about 426.9186443589.

Adding to 77809991 its sum of digits (50), we get a square (77810041 = 8821²).

It can be divided in two parts, 7780 and 9991, that added together give a palindrome (17771).

The spelling of 77809991 in words is "seventy-seven million, eight hundred nine thousand, nine hundred ninety-one".