721317209 has 2 divisors, whose sum is σ = 721317210. Its totient is φ = 721317208.

The previous prime is 721317199. The next prime is 721317229. The reversal of 721317209 is 902713127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 622752025 + 98565184 = 24955^2 + 9928^2 .

It is an emirp because it is prime and its reverse (902713127) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721317209 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (721317229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360658604 + 360658605.

It is an arithmetic number, because the mean of its divisors is an integer number (360658605).

Almost surely, 2^721317209 is an apocalyptic number.

It is an amenable number.

721317209 is a deficient number, since it is larger than the sum of its proper divisors (1).

721317209 is an equidigital number, since it uses as much as digits as its factorization.

721317209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5292, while the sum is 32.

The square root of 721317209 is about 26857.3492549060. The cubic root of 721317209 is about 896.8271854772.

The spelling of 721317209 in words is "seven hundred twenty-one million, three hundred seventeen thousand, two hundred nine".