9900991 has 4 divisors (see below), whose sum is σ = 10026400. Its totient is φ = 9775584.

The previous prime is 9900959. The next prime is 9901007. The reversal of 9900991 is 1990099.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1990099 = 41 ⋅48539.

It is a cyclic number.

It is not a de Polignac number, because 9900991 - 2⁵ = 9900959 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 9900991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9900931) 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, 62586 + ... + 62743.

It is an arithmetic number, because the mean of its divisors is an integer number (2506600).

Almost surely, 2^9900991 is an apocalyptic number.

9900991 is a deficient number, since it is larger than the sum of its proper divisors (125409).

9900991 is a wasteful number, since it uses less digits than its factorization.

9900991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125408.

The product of its (nonzero) digits is 6561, while the sum is 37.

The square root of 9900991 is about 3146.5840208073. The cubic root of 9900991 is about 214.7300813231.

The spelling of 9900991 in words is "nine million, nine hundred thousand, nine hundred ninety-one".