999999891 has 64 divisors (see below), whose sum is σ = 1766707200. Its totient is φ = 551923200.

The previous prime is 999999883. The next prime is 999999893. The reversal of 999999891 is 198999999.

It is a happy number.

It is not a de Polignac number, because 999999891 - 2³ = 999999883 is a prime.

It is not an unprimeable number, because it can be changed into a prime (999999893) 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 in 63 ways as a sum of consecutive naturals, for example, 153325 + ... + 159713.

It is an arithmetic number, because the mean of its divisors is an integer number (27604800).

Almost surely, 2^999999891 is an apocalyptic number.

999999891 is a deficient number, since it is larger than the sum of its proper divisors (766707309).

999999891 is a wasteful number, since it uses less digits than its factorization.

999999891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6457 (or 6451 counting only the distinct ones).

The product of its digits is 38263752, while the sum is 72.

The square root of 999999891 is about 31622.7748782424. The cubic root of 999999891 is about 999.9999636667. Note that the first 4 decimals are identical.

The spelling of 999999891 in words is "nine hundred ninety-nine million, nine hundred ninety-nine thousand, eight hundred ninety-one".