721765 has 12 divisors (see below), whose sum is σ = 952812. Its totient is φ = 524480.

The previous prime is 721739. The next prime is 721783. The reversal of 721765 is 567127.

It can be written as a sum of positive squares in 2 ways, for example, as 314721 + 407044 = 561^2 + 638^2 .

It is not a de Polignac number, because 721765 - 2⁵ = 721733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9 + ... + 1201.

It is an arithmetic number, because the mean of its divisors is an integer number (79401).

2⁷²¹⁷⁶⁵ is an apocalyptic number.

It is an amenable number.

721765 is a deficient number, since it is larger than the sum of its proper divisors (231047).

721765 is a wasteful number, since it uses less digits than its factorization.

721765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1220 (or 1209 counting only the distinct ones).

The product of its digits is 2940, while the sum is 28.

The square root of 721765 is about 849.5675370446. The cubic root of 721765 is about 89.7012729398.

The spelling of 721765 in words is "seven hundred twenty-one thousand, seven hundred sixty-five".