991321 has 4 divisors (see below), whose sum is σ = 1049652. Its totient is φ = 932992.

The previous prime is 991313. The next prime is 991327. The reversal of 991321 is 123199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 123199 = 17 ⋅7247.

It can be written as a sum of positive squares in 2 ways, for example, as 741321 + 250000 = 861^2 + 500^2 .

It is a cyclic number.

It is not a de Polignac number, because 991321 - 2³ = 991313 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991327) 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, 29140 + ... + 29173.

It is an arithmetic number, because the mean of its divisors is an integer number (262413).

2⁹⁹¹³²¹ is an apocalyptic number.

It is an amenable number.

991321 is a deficient number, since it is larger than the sum of its proper divisors (58331).

991321 is a wasteful number, since it uses less digits than its factorization.

991321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58330.

The product of its digits is 486, while the sum is 25.

The square root of 991321 is about 995.6510432878. The cubic root of 991321 is about 99.7098589961.

The spelling of 991321 in words is "nine hundred ninety-one thousand, three hundred twenty-one".