721939 has 4 divisors (see below), whose sum is σ = 764424. Its totient is φ = 679456.

The previous prime is 721921. The next prime is 721951. The reversal of 721939 is 939127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 939127 = 7 ⋅134161.

It is not a de Polignac number, because 721939 - 2¹³ = 713747 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 self number, because there is not a number n which added to its sum of digits gives 721939.

It is not an unprimeable number, because it can be changed into a prime (721909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21217 + ... + 21250.

It is an arithmetic number, because the mean of its divisors is an integer number (191106).

2⁷²¹⁹³⁹ is an apocalyptic number.

721939 is a deficient number, since it is larger than the sum of its proper divisors (42485).

721939 is a wasteful number, since it uses less digits than its factorization.

721939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42484.

The product of its digits is 3402, while the sum is 31.

The square root of 721939 is about 849.6699359163. The cubic root of 721939 is about 89.7084806262.

The spelling of 721939 in words is "seven hundred twenty-one thousand, nine hundred thirty-nine".