721666013 has 2 divisors, whose sum is σ = 721666014. Its totient is φ = 721666012.

The previous prime is 721665983. The next prime is 721666021. The reversal of 721666013 is 310666127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 720546649 + 1119364 = 26843^2 + 1058^2 .

It is an emirp because it is prime and its reverse (310666127) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 721666013 - 2⁶ = 721665949 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721666063) 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, 360833006 + 360833007.

It is an arithmetic number, because the mean of its divisors is an integer number (360833007).

Almost surely, 2^721666013 is an apocalyptic number.

It is an amenable number.

721666013 is a deficient number, since it is larger than the sum of its proper divisors (1).

721666013 is an equidigital number, since it uses as much as digits as its factorization.

721666013 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 32.

The square root of 721666013 is about 26863.8421116563. The cubic root of 721666013 is about 896.9717203627.

The spelling of 721666013 in words is "seven hundred twenty-one million, six hundred sixty-six thousand, thirteen".