9999921 has 4 divisors (see below), whose sum is σ = 13333232. Its totient is φ = 6666612.

The previous prime is 9999907. The next prime is 9999929. The reversal of 9999921 is 1299999.

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 9999921 - 2⁵ = 9999889 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (9999929) 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, 1666651 + ... + 1666656.

It is an arithmetic number, because the mean of its divisors is an integer number (3333308).

Almost surely, 2^9999921 is an apocalyptic number.

It is an amenable number.

9999921 is a deficient number, since it is larger than the sum of its proper divisors (3333311).

9999921 is a wasteful number, since it uses less digits than its factorization.

9999921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3333310.

The product of its digits is 118098, while the sum is 48.

The square root of 9999921 is about 3162.2651691470. The cubic root of 9999921 is about 215.4429016672.

The spelling of 9999921 in words is "nine million, nine hundred ninety-nine thousand, nine hundred twenty-one".