9931721 has 4 divisors (see below), whose sum is σ = 9955092. Its totient is φ = 9908352.

The previous prime is 9931709. The next prime is 9931741. The reversal of 9931721 is 1271399.

It is a happy number.

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 1729225 + 8202496 = 1315^2 + 2864^2 .

It is a cyclic number.

It is not a de Polignac number, because 9931721 - 2¹⁸ = 9669577 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9931741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11036 + ... + 11901.

It is an arithmetic number, because the mean of its divisors is an integer number (2488773).

Almost surely, 2^9931721 is an apocalyptic number.

It is an amenable number.

9931721 is a deficient number, since it is larger than the sum of its proper divisors (23371).

9931721 is a wasteful number, since it uses less digits than its factorization.

9931721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23370.

The product of its digits is 3402, while the sum is 32.

The square root of 9931721 is about 3151.4633109081. The cubic root of 9931721 is about 214.9520065941.

The spelling of 9931721 in words is "nine million, nine hundred thirty-one thousand, seven hundred twenty-one".