721537 has 4 divisors (see below), whose sum is σ = 741076. Its totient is φ = 702000.

The previous prime is 721529. The next prime is 721547. The reversal of 721537 is 735127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 735127 = 47 ⋅15641.

It can be written as a sum of positive squares in 2 ways, for example, as 531441 + 190096 = 729^2 + 436^2 .

It is a cyclic number.

It is not a de Polignac number, because 721537 - 2³ = 721529 is a prime.

It is a Duffinian 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 3 ways as a sum of consecutive naturals, for example, 9714 + ... + 9787.

It is an arithmetic number, because the mean of its divisors is an integer number (185269).

2⁷²¹⁵³⁷ is an apocalyptic number.

It is an amenable number.

721537 is a deficient number, since it is larger than the sum of its proper divisors (19539).

721537 is a wasteful number, since it uses less digits than its factorization.

721537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19538.

The product of its digits is 1470, while the sum is 25.

The square root of 721537 is about 849.4333405277. The cubic root of 721537 is about 89.6918266315.

The spelling of 721537 in words is "seven hundred twenty-one thousand, five hundred thirty-seven".