721643 has 4 divisors (see below), whose sum is σ = 777168. Its totient is φ = 666120.

The previous prime is 721631. The next prime is 721661. The reversal of 721643 is 346127.

721643 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 721643 - 2⁸ = 721387 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721643.

It is not an unprimeable number, because it can be changed into a prime (721613) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27743 + ... + 27768.

It is an arithmetic number, because the mean of its divisors is an integer number (194292).

2⁷²¹⁶⁴³ is an apocalyptic number.

721643 is a deficient number, since it is larger than the sum of its proper divisors (55525).

721643 is a wasteful number, since it uses less digits than its factorization.

721643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55524.

The product of its digits is 1008, while the sum is 23.

The square root of 721643 is about 849.4957327733. The cubic root of 721643 is about 89.6962185837.

The spelling of 721643 in words is "seven hundred twenty-one thousand, six hundred forty-three".