721565 has 16 divisors (see below), whose sum is σ = 988848. Its totient is φ = 500736.

The previous prime is 721561. The next prime is 721571. The reversal of 721565 is 565127.

It can be written as a sum of positive squares in 8 ways, for example, as 47524 + 674041 = 218^2 + 821^2 .

It is a cyclic number.

It is not a de Polignac number, because 721565 - 2² = 721561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721561) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 779 + ... + 1431.

It is an arithmetic number, because the mean of its divisors is an integer number (61803).

2⁷²¹⁵⁶⁵ is an apocalyptic number.

It is an amenable number.

721565 is a deficient number, since it is larger than the sum of its proper divisors (267283).

721565 is a wasteful number, since it uses less digits than its factorization.

721565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 688.

The product of its digits is 2100, while the sum is 26.

The square root of 721565 is about 849.4498219436. The cubic root of 721565 is about 89.6929868116.

The spelling of 721565 in words is "seven hundred twenty-one thousand, five hundred sixty-five".