721391 has 4 divisors (see below), whose sum is σ = 786984. Its totient is φ = 655800.

The previous prime is 721387. The next prime is 721397. The reversal of 721391 is 193127.

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

It is a cyclic number.

It is not a de Polignac number, because 721391 - 2² = 721387 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721397) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32780 + ... + 32801.

It is an arithmetic number, because the mean of its divisors is an integer number (196746).

2⁷²¹³⁹¹ is an apocalyptic number.

721391 is a deficient number, since it is larger than the sum of its proper divisors (65593).

721391 is a wasteful number, since it uses less digits than its factorization.

721391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65592.

The product of its digits is 378, while the sum is 23.

The square root of 721391 is about 849.3473965345. The cubic root of 721391 is about 89.6857766345.

The spelling of 721391 in words is "seven hundred twenty-one thousand, three hundred ninety-one".