91090991 has 4 divisors (see below), whose sum is σ = 91992984. Its totient is φ = 90189000.

The previous prime is 91090957. The next prime is 91091023. The reversal of 91090991 is 19909019.

It is a happy number.

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 91090991 - 2¹⁸ = 90828847 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 (91090291) 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, 450845 + ... + 451046.

It is an arithmetic number, because the mean of its divisors is an integer number (22998246).

Almost surely, 2^91090991 is an apocalyptic number.

91090991 is a deficient number, since it is larger than the sum of its proper divisors (901993).

91090991 is a wasteful number, since it uses less digits than its factorization.

91090991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 901992.

The product of its (nonzero) digits is 6561, while the sum is 38.

The square root of 91090991 is about 9544.1600468559. The cubic root of 91090991 is about 449.9440111412.

The spelling of 91090991 in words is "ninety-one million, ninety thousand, nine hundred ninety-one".