991177221 has 16 divisors (see below), whose sum is σ = 1358881920. Its totient is φ = 642358080.

The previous prime is 991177211. The next prime is 991177223. The reversal of 991177221 is 122771199.

It is not a de Polignac number, because 991177221 - 2¹¹ = 991175173 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 991177221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991177223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11265 + ... + 45926.

It is an arithmetic number, because the mean of its divisors is an integer number (84930120).

Almost surely, 2^991177221 is an apocalyptic number.

It is an amenable number.

991177221 is a deficient number, since it is larger than the sum of its proper divisors (367704699).

991177221 is a wasteful number, since it uses less digits than its factorization.

991177221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57356.

The product of its digits is 15876, while the sum is 39.

The square root of 991177221 is about 31482.9671568612. The cubic root of 991177221 is about 997.0503819743.

The spelling of 991177221 in words is "nine hundred ninety-one million, one hundred seventy-seven thousand, two hundred twenty-one".