721581 has 8 divisors (see below), whose sum is σ = 1099584. Its totient is φ = 412320.

The previous prime is 721577. The next prime is 721597. The reversal of 721581 is 185127.

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

It is not a de Polignac number, because 721581 - 2² = 721577 is a prime.

It is a super-2 number, since 2×721581² = 1041358279122, which contains 22 as substring.

721581 is a lucky 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 721581.

It is not an unprimeable number, because it can be changed into a prime (721561) 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, 17160 + ... + 17201.

It is an arithmetic number, because the mean of its divisors is an integer number (137448).

2⁷²¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

721581 is a deficient number, since it is larger than the sum of its proper divisors (378003).

721581 is a wasteful number, since it uses less digits than its factorization.

721581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34371.

The product of its digits is 560, while the sum is 24.

The square root of 721581 is about 849.4592397520. The cubic root of 721581 is about 89.6936497582.

It can be divided in two parts, 72 and 1581, that added together give a triangular number (1653 = T₅₇).

The spelling of 721581 in words is "seven hundred twenty-one thousand, five hundred eighty-one".