99999999921 has 16 divisors (see below), whose sum is σ = 135946709568. Its totient is φ = 65366875200.

The previous prime is 99999999907. The next prime is 99999999943. The reversal of 99999999921 is 12999999999.

It is not a de Polignac number, because 99999999921 - 2⁹ = 99999999409 is a prime.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (99999999821) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 803895 + ... + 919916.

It is an arithmetic number, because the mean of its divisors is an integer number (8496669348).

Almost surely, 2^99999999921 is an apocalyptic number.

It is an amenable number.

99999999921 is a deficient number, since it is larger than the sum of its proper divisors (35946709647).

99999999921 is a wasteful number, since it uses less digits than its factorization.

99999999921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1724192.

The product of its digits is 774840978, while the sum is 84.

The spelling of 99999999921 in words is "ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred twenty-one".