991205311 has 4 divisors (see below), whose sum is σ = 1009907352. Its totient is φ = 972503272.

The previous prime is 991205233. The next prime is 991205323. The reversal of 991205311 is 113502199.

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 991205311 - 2¹⁵ = 991172543 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 (991205911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9350941 + ... + 9351046.

It is an arithmetic number, because the mean of its divisors is an integer number (252476838).

Almost surely, 2^991205311 is an apocalyptic number.

991205311 is a deficient number, since it is larger than the sum of its proper divisors (18702041).

991205311 is a wasteful number, since it uses less digits than its factorization.

991205311 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18702040.

The product of its (nonzero) digits is 2430, while the sum is 31.

The square root of 991205311 is about 31483.4132679416. The cubic root of 991205311 is about 997.0598007005.

The spelling of 991205311 in words is "nine hundred ninety-one million, two hundred five thousand, three hundred eleven".