991983191 has 4 divisors (see below), whose sum is σ = 993484584. Its totient is φ = 990481800.

The previous prime is 991983163. The next prime is 991983241. The reversal of 991983191 is 191389199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 191389199 = 9109 ⋅21011.

It is a cyclic number.

It is not a de Polignac number, because 991983191 - 2²² = 987788887 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 (991983101) 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, 749705 + ... + 751026.

It is an arithmetic number, because the mean of its divisors is an integer number (248371146).

Almost surely, 2^991983191 is an apocalyptic number.

991983191 is a deficient number, since it is larger than the sum of its proper divisors (1501393).

991983191 is a wasteful number, since it uses less digits than its factorization.

991983191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1501392.

The product of its digits is 157464, while the sum is 50.

The square root of 991983191 is about 31495.7646517750. The cubic root of 991983191 is about 997.3205573326.

The spelling of 991983191 in words is "nine hundred ninety-one million, nine hundred eighty-three thousand, one hundred ninety-one".