721686 has 16 divisors (see below), whose sum is σ = 1649664. Its totient is φ = 206184.

The previous prime is 721663. The next prime is 721687. The reversal of 721686 is 686127.

It is a happy number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721686.

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

721686 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8550 + ... + 8633.

It is an arithmetic number, because the mean of its divisors is an integer number (103104).

2⁷²¹⁶⁸⁶ is an apocalyptic number.

721686 is an abundant number, since it is smaller than the sum of its proper divisors (927978).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

721686 is a wasteful number, since it uses less digits than its factorization.

721686 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17195.

The product of its digits is 4032, while the sum is 30.

The square root of 721686 is about 849.5210415287. The cubic root of 721686 is about 89.6980001021.

The spelling of 721686 in words is "seven hundred twenty-one thousand, six hundred eighty-six".