721000009 has 2 divisors, whose sum is σ = 721000010. Its totient is φ = 721000008.

The previous prime is 720999997. The next prime is 721000051. The reversal of 721000009 is 900000127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 636451984 + 84548025 = 25228^2 + 9195^2 .

It is a cyclic number.

It is not a de Polignac number, because 721000009 - 2⁵ = 720999977 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 721000009.

It is not a weakly prime, because it can be changed into another prime (721000109) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360500004 + 360500005.

It is an arithmetic number, because the mean of its divisors is an integer number (360500005).

Almost surely, 2^721000009 is an apocalyptic number.

It is an amenable number.

721000009 is a deficient number, since it is larger than the sum of its proper divisors (1).

721000009 is an equidigital number, since it uses as much as digits as its factorization.

721000009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 126, while the sum is 19.

The square root of 721000009 is about 26851.4433317839. The cubic root of 721000009 is about 896.6957059704.

The spelling of 721000009 in words is "seven hundred twenty-one million, nine", and thus it is an aban number.