721745221 has 4 divisors (see below), whose sum is σ = 753125472. Its totient is φ = 690364972.

The previous prime is 721745197. The next prime is 721745237. The reversal of 721745221 is 122547127.

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.

It is a cyclic number.

It is not a de Polignac number, because 721745221 - 2¹⁷ = 721614149 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721745291) 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, 15690091 + ... + 15690136.

It is an arithmetic number, because the mean of its divisors is an integer number (188281368).

Almost surely, 2^721745221 is an apocalyptic number.

It is an amenable number.

721745221 is a deficient number, since it is larger than the sum of its proper divisors (31380251).

721745221 is a wasteful number, since it uses less digits than its factorization.

721745221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31380250.

The product of its digits is 7840, while the sum is 31.

The square root of 721745221 is about 26865.3163204903. The cubic root of 721745221 is about 897.0045355134.

The spelling of 721745221 in words is "seven hundred twenty-one million, seven hundred forty-five thousand, two hundred twenty-one".