999999999999921 has 4 divisors (see below), whose sum is σ = 1333333333333232. Its totient is φ = 666666666666612.

The previous prime is 999999999999883. The next prime is 999999999999947. The reversal of 999999999999921 is 129999999999999.

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 999999999999921 - 2⁹ = 999999999999409 is a prime.

It is a super-9 number, since 9×999999999999921⁹ (a number of 136 digits) contains 999999999 as substring.

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 (999999999999521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166666666666651 + ... + 166666666666656.

It is an arithmetic number, because the mean of its divisors is an integer number (333333333333308).

Almost surely, 2^{999999999999921} is an apocalyptic number.

It is an amenable number.

999999999999921 is a deficient number, since it is larger than the sum of its proper divisors (333333333333311).

999999999999921 is a wasteful number, since it uses less digits than its factorization.

999999999999921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333333333333310.

The product of its digits is 5083731656658, while the sum is 120.

The spelling of 999999999999921 in words is "nine hundred ninety-nine trillion, nine hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred twenty-one".