991397977 has 4 divisors (see below), whose sum is σ = 993567796. Its totient is φ = 989228160.

The previous prime is 991397951. The next prime is 991397983. The reversal of 991397977 is 779793199.

991397977 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 2 ways, for example, as 685182976 + 306215001 = 26176^2 + 17499^2 .

It is a cyclic number.

It is not a de Polignac number, because 991397977 - 2²⁷ = 857180249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991397947) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1084224 + ... + 1085137.

It is an arithmetic number, because the mean of its divisors is an integer number (248391949).

Almost surely, 2^991397977 is an apocalyptic number.

It is an amenable number.

991397977 is a deficient number, since it is larger than the sum of its proper divisors (2169819).

991397977 is a wasteful number, since it uses less digits than its factorization.

991397977 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2169818.

The product of its digits is 6751269, while the sum is 61.

The square root of 991397977 is about 31486.4729209227. The cubic root of 991397977 is about 997.1243978384.

The spelling of 991397977 in words is "nine hundred ninety-one million, three hundred ninety-seven thousand, nine hundred seventy-seven".