91810991 has 4 divisors (see below), whose sum is σ = 91831392. Its totient is φ = 91790592.

The previous prime is 91810987. The next prime is 91810997. The reversal of 91810991 is 19901819.

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 91810991 - 2² = 91810987 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 (91810997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 146 + ... + 13551.

It is an arithmetic number, because the mean of its divisors is an integer number (22957848).

Almost surely, 2^91810991 is an apocalyptic number.

91810991 is a deficient number, since it is larger than the sum of its proper divisors (20401).

91810991 is a wasteful number, since it uses less digits than its factorization.

91810991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20400.

The product of its (nonzero) digits is 5832, while the sum is 38.

The square root of 91810991 is about 9581.8052057011. The cubic root of 91810991 is about 451.1263815279.

The spelling of 91810991 in words is "ninety-one million, eight hundred ten thousand, nine hundred ninety-one".