721665613 has 2 divisors, whose sum is σ = 721665614. Its totient is φ = 721665612.

The previous prime is 721665611. The next prime is 721665653. The reversal of 721665613 is 316566127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 688695049 + 32970564 = 26243^2 + 5742^2 .

It is a cyclic number.

It is not a de Polignac number, because 721665613 - 2¹ = 721665611 is a prime.

Together with 721665611, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721665611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360832806 + 360832807.

It is an arithmetic number, because the mean of its divisors is an integer number (360832807).

Almost surely, 2^721665613 is an apocalyptic number.

It is an amenable number.

721665613 is a deficient number, since it is larger than the sum of its proper divisors (1).

721665613 is an equidigital number, since it uses as much as digits as its factorization.

721665613 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45360, while the sum is 37.

The square root of 721665613 is about 26863.8346667039. The cubic root of 721665613 is about 896.9715546403.

The spelling of 721665613 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, six hundred thirteen".