721665617 has 8 divisors (see below), whose sum is σ = 728198016. Its totient is φ = 715159872.

The previous prime is 721665613. The next prime is 721665653. The reversal of 721665617 is 716566127.

721665617 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 721665617 - 2² = 721665613 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721665611) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 49868 + ... + 62690.

It is an arithmetic number, because the mean of its divisors is an integer number (91024752).

Almost surely, 2^721665617 is an apocalyptic number.

It is an amenable number.

721665617 is a deficient number, since it is larger than the sum of its proper divisors (6532399).

721665617 is a wasteful number, since it uses less digits than its factorization.

721665617 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13327.

The product of its digits is 105840, while the sum is 41.

The square root of 721665617 is about 26863.8347411534. The cubic root of 721665617 is about 896.9715562975.

The spelling of 721665617 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, six hundred seventeen".