999999921 has 4 divisors (see below), whose sum is σ = 1333333232. Its totient is φ = 666666612.

The previous prime is 999999893. The next prime is 999999929. The reversal of 999999921 is 129999999.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 999999921 - 2²⁷ = 865782193 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (999999929) 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 3 ways as a sum of consecutive naturals, for example, 166666651 + ... + 166666656.

It is an arithmetic number, because the mean of its divisors is an integer number (333333308).

Almost surely, 2^999999921 is an apocalyptic number.

It is an amenable number.

999999921 is a deficient number, since it is larger than the sum of its proper divisors (333333311).

999999921 is a wasteful number, since it uses less digits than its factorization.

999999921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333333310.

The product of its digits is 9565938, while the sum is 66.

The square root of 999999921 is about 31622.7753525841. The cubic root of 999999921 is about 999.9999736667. Note that the first 4 decimals are identical.

The spelling of 999999921 in words is "nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred twenty-one".