721999721 has 8 divisors (see below), whose sum is σ = 734421000. Its totient is φ = 709597440.

The previous prime is 721999717. The next prime is 721999771. The reversal of 721999721 is 127999127.

721999721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 3759721 + 718240000 = 1939^2 + 26800^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 721999721 - 2² = 721999717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721999771) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86855 + ... + 94803.

It is an arithmetic number, because the mean of its divisors is an integer number (91802625).

Almost surely, 2^721999721 is an apocalyptic number.

It is an amenable number.

721999721 is a deficient number, since it is larger than the sum of its proper divisors (12421279).

721999721 is a wasteful number, since it uses less digits than its factorization.

721999721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9499.

The product of its digits is 142884, while the sum is 47.

The square root of 721999721 is about 26870.0524934359. The cubic root of 721999721 is about 897.1099562908.

The spelling of 721999721 in words is "seven hundred twenty-one million, nine hundred ninety-nine thousand, seven hundred twenty-one".