91000991 has 4 divisors (see below), whose sum is σ = 91020072. Its totient is φ = 90981912.

The previous prime is 91000981. The next prime is 91000999. The reversal of 91000991 is 19900019.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 19900019 = 73 ⋅272603.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-91000991 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 (91000999) 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, 4616 + ... + 14258.

It is an arithmetic number, because the mean of its divisors is an integer number (22755018).

Almost surely, 2^91000991 is an apocalyptic number.

91000991 is a deficient number, since it is larger than the sum of its proper divisors (19081).

91000991 is an equidigital number, since it uses as much as digits as its factorization.

91000991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19080.

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

The square root of 91000991 is about 9539.4439565417. The cubic root of 91000991 is about 449.7957772908.

The spelling of 91000991 in words is "ninety-one million, nine hundred ninety-one", and thus it is an aban number.