9999721 has 4 divisors (see below), whose sum is σ = 10006272. Its totient is φ = 9993172.

The previous prime is 9999713. The next prime is 9999739. The reversal of 9999721 is 1279999.

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, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1279999 = 7 ⋅182857.

It is a cyclic number.

It is not a de Polignac number, because 9999721 - 2³ = 9999713 is a prime.

It is an Ulam number.

It is a Duffinian number.

9999721 is a lucky number.

It is a nialpdrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (9999761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 360 + ... + 4486.

It is an arithmetic number, because the mean of its divisors is an integer number (2501568).

Almost surely, 2^9999721 is an apocalyptic number.

It is an amenable number.

9999721 is a deficient number, since it is larger than the sum of its proper divisors (6551).

9999721 is a wasteful number, since it uses less digits than its factorization.

9999721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6550.

The product of its digits is 91854, while the sum is 46.

The square root of 9999721 is about 3162.2335460873. The cubic root of 9999721 is about 215.4414653603.

The spelling of 9999721 in words is "nine million, nine hundred ninety-nine thousand, seven hundred twenty-one".