721540 has 24 divisors (see below), whose sum is σ = 1552320. Its totient is φ = 281568.

The previous prime is 721529. The next prime is 721547. The reversal of 721540 is 45127.

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (721547) 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, 441 + ... + 1279.

It is an arithmetic number, because the mean of its divisors is an integer number (64680).

2⁷²¹⁵⁴⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 721540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (776160).

721540 is an abundant number, since it is smaller than the sum of its proper divisors (830780).

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

721540 is a wasteful number, since it uses less digits than its factorization.

721540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 891 (or 889 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 19.

The square root of 721540 is about 849.4351064090. The cubic root of 721540 is about 89.6919509379.

Adding to 721540 its reverse (45127), we get a palindrome (766667).

The spelling of 721540 in words is "seven hundred twenty-one thousand, five hundred forty".