991172878177 has 4 divisors (see below), whose sum is σ = 991311336640. Its totient is φ = 991034419716.

The previous prime is 991172878139. The next prime is 991172878247. The reversal of 991172878177 is 771878271199.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 771878271199 = 7 ⋅110268324457.

It is a cyclic number.

It is not a de Polignac number, because 991172878177 - 2²³ = 991164489569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991172878117) 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, 69218493 + ... + 69232810.

It is an arithmetic number, because the mean of its divisors is an integer number (247827834160).

Almost surely, 2^991172878177 is an apocalyptic number.

It is an amenable number.

991172878177 is a deficient number, since it is larger than the sum of its proper divisors (138458463).

991172878177 is a wasteful number, since it uses less digits than its factorization.

991172878177 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138458462.

The product of its digits is 24893568, while the sum is 67.

The spelling of 991172878177 in words is "nine hundred ninety-one billion, one hundred seventy-two million, eight hundred seventy-eight thousand, one hundred seventy-seven".