999915991 has 2 divisors, whose sum is σ = 999915992. Its totient is φ = 999915990.

The previous prime is 999915971. The next prime is 999916031. The reversal of 999915991 is 199519999.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 999915991 - 2¹⁵ = 999883223 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999915901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499957995 + 499957996.

It is an arithmetic number, because the mean of its divisors is an integer number (499957996).

Almost surely, 2^999915991 is an apocalyptic number.

999915991 is a deficient number, since it is larger than the sum of its proper divisors (1).

999915991 is an equidigital number, since it uses as much as digits as its factorization.

999915991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2657205, while the sum is 61.

The square root of 999915991 is about 31621.4482748656. The cubic root of 999915991 is about 999.9719962158.

The spelling of 999915991 in words is "nine hundred ninety-nine million, nine hundred fifteen thousand, nine hundred ninety-one".