991997 has 8 divisors (see below), whose sum is σ = 1022976. Its totient is φ = 961632.

The previous prime is 991987. The next prime is 991999. The reversal of 991997 is 799199.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 991997 - 2⁴ = 991981 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 (991999) 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 7 ways as a sum of consecutive naturals, for example, 7748 + ... + 7874.

It is an arithmetic number, because the mean of its divisors is an integer number (127872).

2⁹⁹¹⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

991997 is a deficient number, since it is larger than the sum of its proper divisors (30979).

991997 is a wasteful number, since it uses less digits than its factorization.

991997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 307.

The product of its digits is 45927, while the sum is 44.

The square root of 991997 is about 995.9904618017. The cubic root of 991997 is about 99.7325185078.

The spelling of 991997 in words is "nine hundred ninety-one thousand, nine hundred ninety-seven".