991391 has 4 divisors (see below), whose sum is σ = 993384. Its totient is φ = 989400.

The previous prime is 991387. The next prime is 991409. The reversal of 991391 is 193199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 193199 = 43 ⋅4493.

It is a cyclic number.

It is not a de Polignac number, because 991391 - 2² = 991387 is a prime.

It is a super-2 number, since 2×991391² = 1965712229762, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991381) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 461 + ... + 1481.

It is an arithmetic number, because the mean of its divisors is an integer number (248346).

2⁹⁹¹³⁹¹ is an apocalyptic number.

991391 is a deficient number, since it is larger than the sum of its proper divisors (1993).

991391 is a wasteful number, since it uses less digits than its factorization.

991391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1992.

The product of its digits is 2187, while the sum is 32.

The square root of 991391 is about 995.6861955456. The cubic root of 991391 is about 99.7122058733.

The spelling of 991391 in words is "nine hundred ninety-one thousand, three hundred ninety-one".