721742557 has 4 divisors (see below), whose sum is σ = 739346076. Its totient is φ = 704139040.

The previous prime is 721742551. The next prime is 721742579. The reversal of 721742557 is 755247127.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 254274916 + 467467641 = 15946^2 + 21621^2 .

It is a cyclic number.

It is not a de Polignac number, because 721742557 - 2¹⁹ = 721218269 is a prime.

It is a Smith number, since the sum of its digits (40) 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 (721742551) 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, 8801698 + ... + 8801779.

It is an arithmetic number, because the mean of its divisors is an integer number (184836519).

Almost surely, 2^721742557 is an apocalyptic number.

It is an amenable number.

721742557 is a deficient number, since it is larger than the sum of its proper divisors (17603519).

721742557 is a wasteful number, since it uses less digits than its factorization.

721742557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17603518.

The product of its digits is 137200, while the sum is 40.

The square root of 721742557 is about 26865.2667397888. The cubic root of 721742557 is about 897.0034318815.

The spelling of 721742557 in words is "seven hundred twenty-one million, seven hundred forty-two thousand, five hundred fifty-seven".