9001991 has 4 divisors (see below), whose sum is σ = 9475800. Its totient is φ = 8528184.

The previous prime is 9001987. The next prime is 9001999. The reversal of 9001991 is 1991009.

9001991 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1991009 = 997 ⋅1997.

It is a cyclic number.

It is not a de Polignac number, because 9001991 - 2² = 9001987 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 (9001999) 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, 236876 + ... + 236913.

It is an arithmetic number, because the mean of its divisors is an integer number (2368950).

Almost surely, 2^9001991 is an apocalyptic number.

9001991 is a deficient number, since it is larger than the sum of its proper divisors (473809).

9001991 is a wasteful number, since it uses less digits than its factorization.

9001991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 473808.

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

The square root of 9001991 is about 3000.3318149831. The cubic root of 9001991 is about 208.0237198664.

The spelling of 9001991 in words is "nine million, one thousand, nine hundred ninety-one".