999668921 has 4 divisors (see below), whose sum is σ = 999792612. Its totient is φ = 999545232.

The previous prime is 999668911. The next prime is 999668933. The reversal of 999668921 is 129866999.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 135955600 + 863713321 = 11660^2 + 29389^2 .

It is a cyclic number.

It is not a de Polignac number, because 999668921 - 2¹⁸ = 999406777 is a prime.

It is a super-2 number, since 2×999668921² = 1998675903226608482, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (999668911) 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, 48806 + ... + 66191.

It is an arithmetic number, because the mean of its divisors is an integer number (249948153).

Almost surely, 2^999668921 is an apocalyptic number.

It is an amenable number.

999668921 is a deficient number, since it is larger than the sum of its proper divisors (123691).

999668921 is a wasteful number, since it uses less digits than its factorization.

999668921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123690.

The product of its digits is 3779136, while the sum is 59.

The square root of 999668921 is about 31617.5413497002. The cubic root of 999668921 is about 999.8896281518.

The spelling of 999668921 in words is "nine hundred ninety-nine million, six hundred sixty-eight thousand, nine hundred twenty-one".