91128991 has 4 divisors (see below), whose sum is σ = 94271400. Its totient is φ = 87986584.

The previous prime is 91128943. The next prime is 91129021. The reversal of 91128991 is 19982119.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 91128991 - 2¹⁵ = 91096223 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91128491) by changing a digit.

It is an upside-down number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1571161 + ... + 1571218.

It is an arithmetic number, because the mean of its divisors is an integer number (23567850).

Almost surely, 2^91128991 is an apocalyptic number.

91128991 is a deficient number, since it is larger than the sum of its proper divisors (3142409).

91128991 is a wasteful number, since it uses less digits than its factorization.

91128991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3142408.

The product of its digits is 11664, while the sum is 40.

The square root of 91128991 is about 9546.1505854454. The cubic root of 91128991 is about 450.0065694514.

The spelling of 91128991 in words is "ninety-one million, one hundred twenty-eight thousand, nine hundred ninety-one".