721689 has 8 divisors (see below), whose sum is σ = 971520. Its totient is φ = 476496.

The previous prime is 721687. The next prime is 721697. The reversal of 721689 is 986127.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 721689 - 2¹ = 721687 is a prime.

721689 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (721687) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 777 + ... + 1430.

It is an arithmetic number, because the mean of its divisors is an integer number (121440).

2⁷²¹⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

721689 is a deficient number, since it is larger than the sum of its proper divisors (249831).

721689 is a wasteful number, since it uses less digits than its factorization.

721689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2319.

The product of its digits is 6048, while the sum is 33.

The square root of 721689 is about 849.5228072277. The cubic root of 721689 is about 89.6981243914.

The spelling of 721689 in words is "seven hundred twenty-one thousand, six hundred eighty-nine".