9909721 has 4 divisors (see below), whose sum is σ = 9929700. Its totient is φ = 9889744.

The previous prime is 9909719. The next prime is 9909749. The reversal of 9909721 is 1279099.

9909721 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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 5953600 + 3956121 = 2440^2 + 1989^2 .

It is a cyclic number.

It is not a de Polignac number, because 9909721 - 2¹ = 9909719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (9909701) 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, 9226 + ... + 10243.

It is an arithmetic number, because the mean of its divisors is an integer number (2482425).

Almost surely, 2^9909721 is an apocalyptic number.

It is an amenable number.

9909721 is a deficient number, since it is larger than the sum of its proper divisors (19979).

9909721 is a wasteful number, since it uses less digits than its factorization.

9909721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19978.

The product of its (nonzero) digits is 10206, while the sum is 37.

The square root of 9909721 is about 3147.9709337921. The cubic root of 9909721 is about 214.7931740956.

The spelling of 9909721 in words is "nine million, nine hundred nine thousand, seven hundred twenty-one".