9991823 has 4 divisors (see below), whose sum is σ = 10235568. Its totient is φ = 9748080.

The previous prime is 9991811. The next prime is 9991837. The reversal of 9991823 is 3281999.

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 9991823 - 2⁸ = 9991567 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41), and also a Moran number because the ratio is a prime number: 243703 = 9991823 / (9 + 9 + 9 + 1 + 8 + 2 + 3).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9991123) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 121811 + ... + 121892.

It is an arithmetic number, because the mean of its divisors is an integer number (2558892).

Almost surely, 2^9991823 is an apocalyptic number.

9991823 is a deficient number, since it is larger than the sum of its proper divisors (243745).

9991823 is a wasteful number, since it uses less digits than its factorization.

9991823 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 243744.

The product of its digits is 34992, while the sum is 41.

The square root of 9991823 is about 3160.9844985384. The cubic root of 9991823 is about 215.3847302819.

The spelling of 9991823 in words is "nine million, nine hundred ninety-one thousand, eight hundred twenty-three".