915721 has 4 divisors (see below), whose sum is σ = 926100. Its totient is φ = 905344.

The previous prime is 915703. The next prime is 915727. The reversal of 915721 is 127519.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127519 = 7 ⋅18217.

It can be written as a sum of positive squares in 2 ways, for example, as 511225 + 404496 = 715^2 + 636^2 .

It is a cyclic number.

It is not a de Polignac number, because 915721 - 2¹⁵ = 882953 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (915727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5056 + ... + 5233.

It is an arithmetic number, because the mean of its divisors is an integer number (231525).

2⁹¹⁵⁷²¹ is an apocalyptic number.

It is an amenable number.

915721 is a deficient number, since it is larger than the sum of its proper divisors (10379).

915721 is a wasteful number, since it uses less digits than its factorization.

915721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10378.

The product of its digits is 630, while the sum is 25.

The square root of 915721 is about 956.9331220101. The cubic root of 915721 is about 97.1078617354.

The spelling of 915721 in words is "nine hundred fifteen thousand, seven hundred twenty-one".