721660221 has 6 divisors (see below), whose sum is σ = 1042398110. Its totient is φ = 481106808.

The previous prime is 721660207. The next prime is 721660249. The reversal of 721660221 is 122066127.

721660221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 717704100 + 3956121 = 26790^2 + 1989^2 .

It is not a de Polignac number, because 721660221 - 2⁹ = 721659709 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 (721660201) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 40092226 + ... + 40092243.

Almost surely, 2^721660221 is an apocalyptic number.

It is an amenable number.

721660221 is a deficient number, since it is larger than the sum of its proper divisors (320737889).

721660221 is a wasteful number, since it uses less digits than its factorization.

721660221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80184475 (or 80184472 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 27.

The square root of 721660221 is about 26863.7343085432. The cubic root of 721660221 is about 896.9693206958.

The spelling of 721660221 in words is "seven hundred twenty-one million, six hundred sixty thousand, two hundred twenty-one".