991686591 has 16 divisors (see below), whose sum is σ = 1679046400. Its totient is φ = 566677944.

The previous prime is 991686583. The next prime is 991686629. The reversal of 991686591 is 195686199.

It is not a de Polignac number, because 991686591 - 2³ = 991686583 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 (991686571) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2623321 + ... + 2623698.

It is an arithmetic number, because the mean of its divisors is an integer number (104940400).

Almost surely, 2^991686591 is an apocalyptic number.

991686591 is a deficient number, since it is larger than the sum of its proper divisors (687359809).

991686591 is a wasteful number, since it uses less digits than its factorization.

991686591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5247035 (or 5247029 counting only the distinct ones).

The product of its digits is 1049760, while the sum is 54.

The square root of 991686591 is about 31491.0557301593. The cubic root of 991686591 is about 997.2211488055.

The spelling of 991686591 in words is "nine hundred ninety-one million, six hundred eighty-six thousand, five hundred ninety-one".