999517991 has 4 divisors (see below), whose sum is σ = 1000020000. Its totient is φ = 999015984.

The previous prime is 999517951. The next prime is 999517999. The reversal of 999517991 is 199715999.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199715999 = 7 ⋅28530857.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-999517991 is a prime.

It is a Duffinian number.

999517991 is a modest number, since divided by 17991 gives 9995 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 999517991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (999517999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 248006 + ... + 252003.

It is an arithmetic number, because the mean of its divisors is an integer number (250005000).

Almost surely, 2^999517991 is an apocalyptic number.

999517991 is a deficient number, since it is larger than the sum of its proper divisors (502009).

999517991 is a wasteful number, since it uses less digits than its factorization.

999517991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 502008.

The product of its digits is 2066715, while the sum is 59.

The square root of 999517991 is about 31615.1544516234. The cubic root of 999517991 is about 999.8393045117.

The spelling of 999517991 in words is "nine hundred ninety-nine million, five hundred seventeen thousand, nine hundred ninety-one".