991571691 has 8 divisors (see below), whose sum is σ = 1442286144. Its totient is φ = 600952520.

The previous prime is 991571689. The next prime is 991571743. The reversal of 991571691 is 196175199.

It is a happy number.

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 991571691 - 2¹ = 991571689 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991571691.

It is not an unprimeable number, because it can be changed into a prime (991571671) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15023781 + ... + 15023846.

It is an arithmetic number, because the mean of its divisors is an integer number (180285768).

Almost surely, 2^991571691 is an apocalyptic number.

991571691 is a deficient number, since it is larger than the sum of its proper divisors (450714453).

991571691 is a wasteful number, since it uses less digits than its factorization.

991571691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30047641.

The product of its digits is 153090, while the sum is 48.

The square root of 991571691 is about 31489.2313497805. The cubic root of 991571691 is about 997.1826335674.

The spelling of 991571691 in words is "nine hundred ninety-one million, five hundred seventy-one thousand, six hundred ninety-one".