721909 has 2 divisors, whose sum is σ = 721910. Its totient is φ = 721908.

The previous prime is 721891. The next prime is 721921. The reversal of 721909 is 909127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 675684 + 46225 = 822^2 + 215^2 .

It is a cyclic number.

It is not a de Polignac number, because 721909 - 2⁹ = 721397 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721979) 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 as a sum of consecutive naturals, namely, 360954 + 360955.

It is an arithmetic number, because the mean of its divisors is an integer number (360955).

2⁷²¹⁹⁰⁹ is an apocalyptic number.

It is an amenable number.

721909 is a deficient number, since it is larger than the sum of its proper divisors (1).

721909 is an equidigital number, since it uses as much as digits as its factorization.

721909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1134, while the sum is 28.

The square root of 721909 is about 849.6522818189. The cubic root of 721909 is about 89.7072380043.

The spelling of 721909 in words is "seven hundred twenty-one thousand, nine hundred nine".