721665773 has 4 divisors (see below), whose sum is σ = 722930208. Its totient is φ = 720401340.

The previous prime is 721665767. The next prime is 721665781. The reversal of 721665773 is 377566127.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 377566127 = 1949 ⋅193723.

It is a cyclic number.

It is not a de Polignac number, because 721665773 - 2²⁰ = 720617197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721665073) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 631361 + ... + 632502.

It is an arithmetic number, because the mean of its divisors is an integer number (180732552).

Almost surely, 2^721665773 is an apocalyptic number.

It is an amenable number.

721665773 is a deficient number, since it is larger than the sum of its proper divisors (1264435).

721665773 is a wasteful number, since it uses less digits than its factorization.

721665773 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1264434.

The product of its digits is 370440, while the sum is 44.

The square root of 721665773 is about 26863.8376446851. The cubic root of 721665773 is about 896.9716209292.

The spelling of 721665773 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, seven hundred seventy-three".