991090991 has 16 divisors (see below), whose sum is σ = 1137513888. Its totient is φ = 855244800.

The previous prime is 991090967. The next prime is 991091009. The reversal of 991090991 is 199090199.

It is a cyclic number.

It is not a de Polignac number, because 991090991 - 2¹⁴ = 991074607 is a prime.

It is a super-2 number, since 2×991090991² = 1964522704882724162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991090931) 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 15 ways as a sum of consecutive naturals, for example, 13010 + ... + 46383.

It is an arithmetic number, because the mean of its divisors is an integer number (71094618).

Almost surely, 2^991090991 is an apocalyptic number.

991090991 is a deficient number, since it is larger than the sum of its proper divisors (146422897).

991090991 is a wasteful number, since it uses less digits than its factorization.

991090991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59482.

The product of its (nonzero) digits is 59049, while the sum is 47.

The square root of 991090991 is about 31481.5976564087. The cubic root of 991090991 is about 997.0214674856.

The spelling of 991090991 in words is "nine hundred ninety-one million, ninety thousand, nine hundred ninety-one".