721531 has 4 divisors (see below), whose sum is σ = 763992. Its totient is φ = 679072.

The previous prime is 721529. The next prime is 721547. The reversal of 721531 is 135127.

721531 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, and also an emirpimes, since its reverse is a distinct semiprime: 135127 = 163 ⋅829.

It is a cyclic number.

It is not a de Polignac number, because 721531 - 2¹ = 721529 is a prime.

It is a super-2 number, since 2×721531² = 1041213967922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 721499 and 721508.

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 3 ways as a sum of consecutive naturals, for example, 21205 + ... + 21238.

It is an arithmetic number, because the mean of its divisors is an integer number (190998).

2⁷²¹⁵³¹ is an apocalyptic number.

721531 is a deficient number, since it is larger than the sum of its proper divisors (42461).

721531 is a wasteful number, since it uses less digits than its factorization.

721531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42460.

The product of its digits is 210, while the sum is 19.

The square root of 721531 is about 849.4298087541. The cubic root of 721531 is about 89.6915780175.

Adding to 721531 its reverse (135127), we get a palindrome (856658).

The spelling of 721531 in words is "seven hundred twenty-one thousand, five hundred thirty-one".