999855991 has 2 divisors, whose sum is σ = 999855992.
Its totient is φ = 999855990.
The previous prime is 999855973. The next prime is 999856021. The reversal of 999855991 is 199558999.
It is a weak prime.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-999855991 is a prime.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (999855911) 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 as a sum of consecutive naturals, namely, 499927995 + 499927996.
It is an arithmetic number, because the mean of its divisors is an integer number (499927996).
Almost surely, 2999855991 is an apocalyptic number.
999855991 is a deficient number, since it is larger than the sum of its proper divisors (1).
999855991 is an equidigital number, since it uses as much as digits as its factorization.
999855991 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 11809800, while the sum is 64.
The square root of 999855991 is about 31620.4995374836.
The cubic root of 999855991 is about 999.9519946955.
The spelling of 999855991 in words is "nine hundred ninety-nine million, eight hundred fifty-five thousand, nine hundred ninety-one".