721557 has 6 divisors (see below), whose sum is σ = 1042262. Its totient is φ = 481032.

The previous prime is 721547. The next prime is 721561. The reversal of 721557 is 755127.

It can be written as a sum of positive squares in only one way, i.e., 527076 + 194481 = 726^2 + 441^2 .

It is not a de Polignac number, because 721557 - 2¹⁹ = 197269 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 721557.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721547) 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, 40078 + ... + 40095.

2⁷²¹⁵⁵⁷ is an apocalyptic number.

It is an amenable number.

721557 is a deficient number, since it is larger than the sum of its proper divisors (320705).

721557 is a wasteful number, since it uses less digits than its factorization.

721557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80179 (or 80176 counting only the distinct ones).

The product of its digits is 2450, while the sum is 27.

The square root of 721557 is about 849.4451130002. The cubic root of 721557 is about 89.6926553346.

The spelling of 721557 in words is "seven hundred twenty-one thousand, five hundred fifty-seven".