721636 has 12 divisors (see below), whose sum is σ = 1306620. Its totient is φ = 348320.

The previous prime is 721631. The next prime is 721661. The reversal of 721636 is 636127.

It can be written as a sum of positive squares in 2 ways, for example, as 168100 + 553536 = 410^2 + 744^2 .

It is an alternating number because its digits alternate between odd and even.

It is a self number, because there is not a number n which added to its sum of digits gives 721636.

It is not an unprimeable number, because it can be changed into a prime (721631) by changing a digit.

721636 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 3 ways as a sum of consecutive naturals, for example, 2995 + ... + 3226.

It is an arithmetic number, because the mean of its divisors is an integer number (108885).

2⁷²¹⁶³⁶ is an apocalyptic number.

It is an amenable number.

721636 is a deficient number, since it is larger than the sum of its proper divisors (584984).

721636 is a wasteful number, since it uses less digits than its factorization.

721636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6254 (or 6252 counting only the distinct ones).

The product of its digits is 1512, while the sum is 25.

The square root of 721636 is about 849.4916126720. The cubic root of 721636 is about 89.6959285624.

The spelling of 721636 in words is "seven hundred twenty-one thousand, six hundred thirty-six".