991599 has 16 divisors (see below), whose sum is σ = 1577472. Its totient is φ = 541728.

The previous prime is 991579. The next prime is 991603. The reversal of 991599 is 995199.

It is not a de Polignac number, because 991599 - 2⁵ = 991567 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991599.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991599.

It is not an unprimeable number, because it can be changed into a prime (991579) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 544 + ... + 1509.

It is an arithmetic number, because the mean of its divisors is an integer number (98592).

2⁹⁹¹⁵⁹⁹ is an apocalyptic number.

991599 is a deficient number, since it is larger than the sum of its proper divisors (585873).

991599 is a wasteful number, since it uses less digits than its factorization.

991599 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2086.

The product of its digits is 32805, while the sum is 42.

The square root of 991599 is about 995.7906406469. The cubic root of 991599 is about 99.7191787994.

Subtracting 991599 from its reverse (995199), we obtain a square (3600 = 60²).

The spelling of 991599 in words is "nine hundred ninety-one thousand, five hundred ninety-nine".