721721909 has 2 divisors, whose sum is σ = 721721910. Its totient is φ = 721721908.

The previous prime is 721721863. The next prime is 721721929. The reversal of 721721909 is 909127127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 373339684 + 348382225 = 19322^2 + 18665^2 .

It is a cyclic number.

It is not a de Polignac number, because 721721909 - 2⁸ = 721721653 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721721929) 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 as a sum of consecutive naturals, namely, 360860954 + 360860955.

It is an arithmetic number, because the mean of its divisors is an integer number (360860955).

Almost surely, 2^721721909 is an apocalyptic number.

It is an amenable number.

721721909 is a deficient number, since it is larger than the sum of its proper divisors (1).

721721909 is an equidigital number, since it uses as much as digits as its factorization.

721721909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15876, while the sum is 38.

The square root of 721721909 is about 26864.8824490263. The cubic root of 721721909 is about 896.9948778141.

The spelling of 721721909 in words is "seven hundred twenty-one million, seven hundred twenty-one thousand, nine hundred nine".