991331 has 4 divisors (see below), whose sum is σ = 1081464. Its totient is φ = 901200.

The previous prime is 991327. The next prime is 991343. The reversal of 991331 is 133199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 133199 = 11 ⋅12109.

It is a cyclic number.

It is not a de Polignac number, because 991331 - 2² = 991327 is a prime.

It is a super-2 number, since 2×991331² = 1965474303122, which contains 22 as substring.

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 991331.

It is not an unprimeable number, because it can be changed into a prime (991381) 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, 45050 + ... + 45071.

It is an arithmetic number, because the mean of its divisors is an integer number (270366).

2⁹⁹¹³³¹ is an apocalyptic number.

991331 is a deficient number, since it is larger than the sum of its proper divisors (90133).

991331 is a wasteful number, since it uses less digits than its factorization.

991331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90132.

The product of its digits is 729, while the sum is 26.

The square root of 991331 is about 995.6560651149. The cubic root of 991331 is about 99.7101942711.

It can be divided in two parts, 99 and 1331, that multiplied together give a square (131769 = 363²).

The spelling of 991331 in words is "nine hundred ninety-one thousand, three hundred thirty-one".