999907721 has 4 divisors (see below), whose sum is σ = 1026932292. Its totient is φ = 972883152.

The previous prime is 999907709. The next prime is 999907739. The reversal of 999907721 is 127709999.

999907721 is digitally balanced in base 2, 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 968143225 + 31764496 = 31115^2 + 5636^2 .

It is a cyclic number.

It is not a de Polignac number, because 999907721 - 2¹⁴ = 999891337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (999907421) 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, 13512230 + ... + 13512303.

It is an arithmetic number, because the mean of its divisors is an integer number (256733073).

Almost surely, 2^999907721 is an apocalyptic number.

It is an amenable number.

999907721 is a deficient number, since it is larger than the sum of its proper divisors (27024571).

999907721 is a wasteful number, since it uses less digits than its factorization.

999907721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27024570.

The product of its (nonzero) digits is 642978, while the sum is 53.

The square root of 999907721 is about 31621.3175089211. The cubic root of 999907721 is about 999.9692393871.

The spelling of 999907721 in words is "nine hundred ninety-nine million, nine hundred seven thousand, seven hundred twenty-one".