721836 has 18 divisors (see below), whose sum is σ = 1824732. Its totient is φ = 240600.

The previous prime is 721793. The next prime is 721843. The reversal of 721836 is 638127.

It is a tau number, because it is divible by the number of its divisors (18).

It is an Ulam number.

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

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721836.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9990 + ... + 10061.

It is an arithmetic number, because the mean of its divisors is an integer number (101374).

2⁷²¹⁸³⁶ is an apocalyptic number.

It is an amenable number.

721836 is an abundant number, since it is smaller than the sum of its proper divisors (1102896).

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

721836 is a wasteful number, since it uses less digits than its factorization.

721836 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20061 (or 20056 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 721836 is about 849.6093219828. The cubic root of 721836 is about 89.7042141471.

The spelling of 721836 in words is "seven hundred twenty-one thousand, eight hundred thirty-six".