991000091 has 4 divisors (see below), whose sum is σ = 1049294232. Its totient is φ = 932705952.

The previous prime is 991000069. The next prime is 991000097. The reversal of 991000091 is 190000199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 190000199 = 29 ⋅6551731.

It is not a de Polignac number, because 991000091 - 2¹⁰ = 990999067 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991000097) 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, 29147045 + ... + 29147078.

It is an arithmetic number, because the mean of its divisors is an integer number (262323558).

Almost surely, 2^991000091 is an apocalyptic number.

991000091 is a deficient number, since it is larger than the sum of its proper divisors (58294141).

991000091 is a wasteful number, since it uses less digits than its factorization.

991000091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58294140.

The product of its (nonzero) digits is 729, while the sum is 29.

The square root of 991000091 is about 31480.1539227495. The cubic root of 991000091 is about 996.9909852449.

The spelling of 991000091 in words is "nine hundred ninety-one million, ninety-one", and thus it is an aban number.